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.

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/components/LoadingState.kt

@@ -25,6 +25,7 @@ import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.text.selection.SelectionContainer
 import androidx.compose.material3.Button
 import androidx.compose.material3.CircularProgressIndicator
 import androidx.compose.material3.MaterialTheme
@@ -66,6 +67,11 @@ fun LoadingState(
 
 /**
  * A centered empty state with title, optional description, and optional refresh action.
+ *
+ * The optional `description` is wrapped in a [SelectionContainer] so users can
+ * select and copy it. `EmptyState` is reused as the in-feed error renderer
+ * (e.g. "Error loading feed" with the underlying error in `description`), so
+ * making the description selectable lets users copy error text for reporting.
  */
 @Composable
 fun EmptyState(
@@ -89,11 +95,13 @@ fun EmptyState(
         )
         if (description != null) {
             Spacer(Modifier.height(8.dp))
-            Text(
-                description,
-                style = MaterialTheme.typography.bodyMedium,
-                color = MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.7f),
-            )
+            SelectionContainer {
+                Text(
+                    description,
+                    style = MaterialTheme.typography.bodyMedium,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.7f),
+                )
+            }
         }
         if (onRefresh != null) {
             Spacer(Modifier.height(16.dp))
@@ -106,6 +114,9 @@ fun EmptyState(
 
 /**
  * A centered error state with message and optional retry action.
+ *
+ * The error `message` is wrapped in a [SelectionContainer] so users can select
+ * and copy it — useful for reporting bugs or pasting error text into a search.
  */
 @Composable
 fun ErrorState(
@@ -121,11 +132,13 @@ fun ErrorState(
         horizontalAlignment = Alignment.CenterHorizontally,
         verticalArrangement = Arrangement.Center,
     ) {
-        Text(
-            message,
-            style = MaterialTheme.typography.bodyMedium,
-            color = MaterialTheme.colorScheme.error,
-        )
+        SelectionContainer {
+            Text(
+                message,
+                style = MaterialTheme.typography.bodyMedium,
+                color = MaterialTheme.colorScheme.error,
+            )
+        }
         if (onRetry != null) {
             Spacer(Modifier.height(16.dp))
             Button(onClick = onRetry) {