fix(multi-account): npub-only login stores ViewOnly type, reactive display names

Root cause of npub-only switch failure:
loginWithKey() with pubkey created AccountState with signerType=Internal
(default). switchAccount then called loadInternalAccount which requires
a private key from SecureKeyStorage → failed. Now sets ViewOnly.

Display names not showing:
- resolveDisplayName() ran at composition time but metadata hadn't
  loaded from relays yet. Dropdown never recomposed when it arrived.
- Added metadataVersion counter to DesktopLocalCache, incremented on
  each consumeMetadata(). Dropdown collects it to trigger recomposition
  when user names become available.

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

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

@@ -536,6 +536,7 @@ class AccountManager internal constructor(
                         npub = keyPair.pubKey.toNpub(),
                         nsec = null,
                         isReadOnly = true,
+                        signerType = SignerType.ViewOnly,
                     )
                 _accountState.value = state
                 Result.success(state)

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/cache/DesktopLocalCache.kt

@@ -78,6 +78,10 @@ class DesktopLocalCache : ICacheProvider {
     private val _followedUsers = MutableStateFlow<Set<HexKey>>(emptySet())
     val followedUsers: StateFlow<Set<HexKey>> = _followedUsers.asStateFlow()
 
+    /** Increments on each metadata update — observe to recompose when user names change. */
+    private val _metadataVersion = MutableStateFlow(0L)
+    val metadataVersion: StateFlow<Long> = _metadataVersion.asStateFlow()
+
     companion object {
     }
 
@@ -151,6 +155,7 @@ class DesktopLocalCache : ICacheProvider {
             val newUserMetadata = event.contactMetaData()
             if (newUserMetadata != null) {
                 user.updateUserInfo(newUserMetadata, event)
+                _metadataVersion.value++
                 // Invalidate metadata flows on notes by this author that have observers
                 // so QuotedNoteEmbed/FeedNoteCard recompose with updated avatar/name
                 notes.forEach { _, note ->

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

@@ -43,6 +43,7 @@ import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
@@ -95,6 +96,10 @@ fun AccountSwitcherDropdown(
     var expanded by remember { mutableStateOf(false) }
     var confirmLogoutNpub by remember { mutableStateOf<String?>(null) }
 
+    // Observe metadata version to recompose when user display names load from relays
+    @Suppress("UNUSED_VARIABLE")
+    val metadataVersion by localCache?.metadataVersion?.collectAsState() ?: remember { mutableStateOf(0L) }
+
     Box(modifier = modifier) {
         IconButton(
             onClick = { expanded = true },