fix(desktop): make error messages selectable so users can copy them

Several user-visible error messages on Desktop are rendered with plain
`Text` composables, which means they can't be selected or copied. That
makes it awkward to share an error in a bug report or paste a hex error
string into a search.

Wrap the error text in `SelectionContainer` at the canonical sites:

- `commons.ui.components.LoadingState`: wrap the description in
  `EmptyState` and the message in `ErrorState`. `EmptyState` is reused
  as the in-feed error renderer (e.g. 'Error loading feed' with the
  underlying error in `description`), so this covers feed/loading
  errors across screens that use these helpers.
- `ComposeNoteDialog`: wrap the validation error and the upload error
  in the compose-note dialog.
- `auth/LoginCard` (Nostr Connect): wrap the connection error.
- `auth/KeyInputField`: wrap the supporting-text error so the inline
  message under the nsec input field can be copied.

No visual changes \u2014 `SelectionContainer` does not affect layout or
styling. Selection works on Compose Desktop (mouse drag) and on Android
(long-press) without further changes.

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

@@ -31,6 +31,7 @@ import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.foundation.text.selection.SelectionContainer
 import androidx.compose.material3.Button
 import androidx.compose.material3.Card
 import androidx.compose.material3.MaterialTheme
@@ -251,20 +252,24 @@ fun ComposeNoteDialog(
 
                 errorMessage?.let { error ->
                     Spacer(Modifier.height(8.dp))
-                    Text(
-                        error,
-                        style = MaterialTheme.typography.bodySmall,
-                        color = MaterialTheme.colorScheme.error,
-                    )
+                    SelectionContainer {
+                        Text(
+                            error,
+                            style = MaterialTheme.typography.bodySmall,
+                            color = MaterialTheme.colorScheme.error,
+                        )
+                    }
                 }
 
                 uploadState.error?.let { error ->
                     Spacer(Modifier.height(4.dp))
-                    Text(
-                        "Upload error: $error",
-                        style = MaterialTheme.typography.bodySmall,
-                        color = MaterialTheme.colorScheme.error,
-                    )
+                    SelectionContainer {
+                        Text(
+                            "Upload error: $error",
+                            style = MaterialTheme.typography.bodySmall,
+                            color = MaterialTheme.colorScheme.error,
+                        )
+                    }
                 }
 
                 Spacer(Modifier.height(8.dp))

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/auth/KeyInputField.kt

@@ -22,6 +22,7 @@ package com.vitorpamplona.amethyst.desktop.ui.auth
 
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.text.selection.SelectionContainer
 import androidx.compose.material3.Card
 import androidx.compose.material3.CardDefaults
 import androidx.compose.material3.IconButton
@@ -85,7 +86,11 @@ fun KeyInputField(
         isError = errorMessage != null,
         supportingText =
             errorMessage?.let {
-                { Text(it, color = MaterialTheme.colorScheme.error) }
+                {
+                    SelectionContainer {
+                        Text(it, color = MaterialTheme.colorScheme.error)
+                    }
+                }
             },
     )
 }

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/auth/LoginCard.kt

@@ -30,6 +30,7 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.foundation.text.selection.SelectionContainer
 import androidx.compose.material3.Button
 import androidx.compose.material3.Card
 import androidx.compose.material3.CardDefaults
@@ -254,11 +255,13 @@ private fun NostrConnectContent(
     val clipboardManager = LocalClipboard.current
 
     if (errorMessage != null) {
-        Text(
-            errorMessage!!,
-            style = MaterialTheme.typography.bodySmall,
-            color = MaterialTheme.colorScheme.error,
-        )
+        SelectionContainer {
+            Text(
+                errorMessage!!,
+                style = MaterialTheme.typography.bodySmall,
+                color = MaterialTheme.colorScheme.error,
+            )
+        }
         Spacer(Modifier.height(12.dp))
         Button(onClick = {
             errorMessage = null