Add search, offline queue, app icon, and UI polish

- Collapsible search in notes and tasks: magnifying glass in AppBar
  expands to a text field inline; close button resets the filter
- Offline capture queue: failed quick-captures (NetworkException) are
  persisted to SharedPreferences and retried automatically on next
  successful submit or app start; badge shows pending count
- App icon: book-with-sparkle logo from FabledAssistant SVG rendered
  at all Android densities with adaptive icon (indigo #6366f1 bg)
- Dark mode subtitle fix: use colorScheme.onSurfaceVariant for note
  preview and conversation timestamp text
- Remove swipe-to-delete (accidental deletions); long-press remains
- Chat: SSE streaming reliability, polling fallback, title patching
- Settings: theme toggle (system/light/dark) persisted to prefs
- Notes: delete button in edit screen; body preview in list
- Tasks: fix delete dialog context; description search support

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/data/repositories/chat_repository.dart

@@ -10,7 +10,7 @@ class ChatRepository {
   Future<Conversation> createConversation(String title) =>
       _api.createConversation(title);
   Future<void> deleteConversation(int id) => _api.deleteConversation(id);
-  Future<List<Message>> getMessages(int conversationId) =>
+  Future<(Conversation, List<Message>)> getMessages(int conversationId) =>
       _api.getMessages(conversationId);
   Future<void> sendMessage(int conversationId, String content) =>
       _api.sendMessage(conversationId, content);