Initial commit: Fabled Android app

Flutter Android client for FabledAssistant with:
- Session-cookie auth via persistent cookie jar (Dio + cookie_jar)
- OAuth/SSO login via in-app WebView (flutter_inappwebview)
- Notes: list, detail (markdown render), create/edit
- Tasks: list with status tabs, create/edit with priority
- Chat: SSE streaming bubbles, conversation management
- Quick Capture FAB for rapid note/task creation
- Settings screen (change server URL, logout)
- Android home screen widget → opens chat
- Riverpod state management, go_router navigation

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

lib/core/exceptions.dart

@@ -0,0 +1,19 @@
+class AppException implements Exception {
+  final String message;
+  const AppException(this.message);
+
+  @override
+  String toString() => message;
+}
+
+class NetworkException extends AppException {
+  const NetworkException(super.message);
+}
+
+class AuthException extends AppException {
+  const AuthException(super.message);
+}
+
+class NotFoundException extends AppException {
+  const NotFoundException(super.message);
+}