feat(multi-account): extract SignerType, AccountInfo, AccountStorage to commons

Phase 1 of multi-account support. Move account types to commons/commonMain
so both Android and Desktop share the same data model:

- SignerType sealed class (Internal, Remote, ViewOnly)
- AccountInfo data class (npub, signerType, isTransient)
- AccountStorage interface (loadAccounts, saveAccount, etc.)

Desktop AccountManager now imports SignerType from commons instead of
defining its own. All existing tests updated with new import path.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/account/AccountInfo.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.model.account
+
+import androidx.compose.runtime.Immutable
+
+/**
+ * Lightweight account metadata for account listing and switching.
+ * Does NOT contain private keys — those are stored in SecureKeyStorage.
+ */
+@Immutable
+data class AccountInfo(
+    val npub: String,
+    val signerType: SignerType,
+    val isTransient: Boolean = false,
+)

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/account/AccountStorage.kt

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.model.account
+
+/**
+ * Platform-agnostic interface for persisting account metadata.
+ * Implementations:
+ * - Android: LocalPreferences (EncryptedSharedPreferences)
+ * - Desktop: DesktopAccountStorage (encrypted JSON file)
+ *
+ * Does NOT handle private key storage — that's SecureKeyStorage's job.
+ * Constructor-injected, not expect/actual.
+ */
+interface AccountStorage {
+    /** Load all saved account metadata */
+    suspend fun loadAccounts(): List<AccountInfo>
+
+    /** Save or update account metadata */
+    suspend fun saveAccount(info: AccountInfo)
+
+    /** Delete account metadata by npub */
+    suspend fun deleteAccount(npub: String)
+
+    /** Get the npub of the currently active account, or null if none */
+    suspend fun currentAccount(): String?
+
+    /** Set which account is currently active */
+    suspend fun setCurrentAccount(npub: String)
+}

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/account/SignerType.kt

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.model.account
+
+import androidx.compose.runtime.Immutable
+
+/**
+ * Represents how an account's signing is handled.
+ * Sealed class (not enum) because Remote carries additional data.
+ */
+@Immutable
+sealed class SignerType {
+    /** Account has a local private key (nsec) */
+    data object Internal : SignerType()
+
+    /** Account uses a NIP-46 remote signer (bunker) */
+    @Immutable
+    data class Remote(
+        val bunkerUri: String,
+    ) : SignerType()
+
+    /** Account is view-only (npub only, no signing capability) */
+    data object ViewOnly : SignerType()
+}

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/Main.kt

@@ -670,7 +670,7 @@ fun App(
             val result = accountManager.loadSavedAccount()
             if (result.isSuccess) {
                 val current = accountManager.currentAccount()
-                if (current?.signerType is com.vitorpamplona.amethyst.desktop.account.SignerType.Remote) {
+                if (current?.signerType is com.vitorpamplona.amethyst.commons.model.account.SignerType.Remote) {
                     accountManager.startHeartbeat(scope)
                 }
             } else if (accountManager.hasBunkerAccount()) {
@@ -702,7 +702,7 @@ fun App(
                         onLoginSuccess = {
                             // Start heartbeat if bunker account
                             val current = accountManager.currentAccount()
-                            if (current?.signerType is com.vitorpamplona.amethyst.desktop.account.SignerType.Remote) {
+                            if (current?.signerType is com.vitorpamplona.amethyst.commons.model.account.SignerType.Remote) {
                                 accountManager.startHeartbeat(scope)
                             }
                         },

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/account/AccountManager.kt

@@ -26,6 +26,7 @@ import com.vitorpamplona.amethyst.commons.domain.nip46.NostrConnectLoginUseCase
 import com.vitorpamplona.amethyst.commons.domain.nip46.SignerConnectionState
 import com.vitorpamplona.amethyst.commons.keystorage.SecureKeyStorage
 import com.vitorpamplona.amethyst.commons.keystorage.SecureStorageException
+import com.vitorpamplona.amethyst.commons.model.account.SignerType
 import com.vitorpamplona.amethyst.desktop.network.DesktopHttpClient
 import com.vitorpamplona.quartz.nip01Core.core.hexToByteArray
 import com.vitorpamplona.quartz.nip01Core.core.toHexKey
@@ -65,14 +66,6 @@ import java.io.File
 import java.nio.file.Files
 import java.nio.file.attribute.PosixFilePermission
 
-sealed class SignerType {
-    data object Internal : SignerType()
-
-    data class Remote(
-        val bunkerUri: String,
-    ) : SignerType()
-}
-
 sealed class AccountState {
     data object LoggedOut : AccountState()
 

desktopApp/src/jvmTest/kotlin/com/vitorpamplona/amethyst/desktop/account/AccountManagerHeartbeatTest.kt

@@ -21,6 +21,7 @@
 package com.vitorpamplona.amethyst.desktop.account
 
 import com.vitorpamplona.amethyst.commons.keystorage.SecureKeyStorage
+import com.vitorpamplona.amethyst.commons.model.account.SignerType
 import com.vitorpamplona.quartz.nip01Core.core.toHexKey
 import com.vitorpamplona.quartz.nip01Core.crypto.KeyPair
 import com.vitorpamplona.quartz.nip01Core.relay.client.EmptyNostrClient

desktopApp/src/jvmTest/kotlin/com/vitorpamplona/amethyst/desktop/account/AccountManagerKeyLoginTest.kt

@@ -21,6 +21,7 @@
 package com.vitorpamplona.amethyst.desktop.account
 
 import com.vitorpamplona.amethyst.commons.keystorage.SecureKeyStorage
+import com.vitorpamplona.amethyst.commons.model.account.SignerType
 import com.vitorpamplona.quartz.nip01Core.crypto.KeyPair
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSignerInternal
 import com.vitorpamplona.quartz.nip19Bech32.toNpub

desktopApp/src/jvmTest/kotlin/com/vitorpamplona/amethyst/desktop/account/AccountManagerLoadAccountTest.kt

@@ -21,6 +21,7 @@
 package com.vitorpamplona.amethyst.desktop.account
 
 import com.vitorpamplona.amethyst.commons.keystorage.SecureKeyStorage
+import com.vitorpamplona.amethyst.commons.model.account.SignerType
 import com.vitorpamplona.quartz.nip01Core.core.toHexKey
 import com.vitorpamplona.quartz.nip01Core.crypto.KeyPair
 import com.vitorpamplona.quartz.nip19Bech32.toNpub

desktopApp/src/jvmTest/kotlin/com/vitorpamplona/amethyst/desktop/account/AccountManagerNip46IsolationTest.kt

@@ -22,6 +22,7 @@ package com.vitorpamplona.amethyst.desktop.account
 
 import com.vitorpamplona.amethyst.commons.domain.nip46.SignerConnectionState
 import com.vitorpamplona.amethyst.commons.keystorage.SecureKeyStorage
+import com.vitorpamplona.amethyst.commons.model.account.SignerType
 import com.vitorpamplona.quartz.nip01Core.core.toHexKey
 import com.vitorpamplona.quartz.nip01Core.crypto.KeyPair
 import com.vitorpamplona.quartz.nip19Bech32.toNpub