feat: app overhaul — Briefing-first navigation, Library, capture queue

Plans 1-3 implemented:

Plan 1 — Foundation
- Add google_fonts ^6.2.1
- lib/core/theme.dart: slate-indigo ColorScheme (dark/light), Fraunces
  headings, GradientButton widget
- lib/providers/capture_work_queue_provider.dart: in-memory sequential
  work queue; CaptureWorkQueueNotifier drains one item at a time;
  captureResultProvider feeds snackbars to UI
- lib/app.dart: wire fabledDarkTheme/fabledLightTheme; replace blocking
  _QuickCaptureBar with queue-based implementation (progress bar, badge)

Plan 2 — Navigation
- 3-tab shell: Briefing · Library · Chat (was Notes · Tasks · Projects · Chat)
- lib/screens/library/library_screen.dart: unified notes+tasks+projects list
  with filter pills, status sub-filter for tasks, live search, FAB
- lib/widgets/library_item_card.dart: NoteLibraryCard, TaskLibraryCard
  (status cycle), ProjectLibraryCard
- lib/screens/chat/conversations_tab_screen.dart: focused replacement for
  ConversationsListScreen
- Delete 5 dead screens: notes_list, tasks_list, project_list,
  conversations_list, quick_capture

Plan 3 — Briefing
- lib/data/models/briefing_conversation.dart
- lib/data/api/briefing_api.dart: getToday, getHistory, getMessages,
  triggerSlot
- lib/providers/briefing_provider.dart: BriefingNotifier with sendReply
  (optimistic + SSE + poll, same pattern as MessagesNotifier) and refresh
- lib/widgets/chat_message_bubble.dart: extracted + redesigned shared bubble
  (ghost user bubbles, left-accent assistant bubbles)
- lib/widgets/briefing_digest_card.dart: expandable first-message card
- lib/screens/briefing/briefing_screen.dart: digest card, conversation list,
  streaming reply bar, refresh button, history overflow menu
- lib/screens/briefing/briefing_history_screen.dart: read-only past dates

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

lib/providers/capture_work_queue_provider.dart

@@ -0,0 +1,98 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../core/exceptions.dart';
+import 'api_client_provider.dart';
+import 'capture_queue_provider.dart';
+import 'notes_provider.dart';
+import 'tasks_provider.dart';
+
+/// Outcome of a single capture attempt — consumed by the UI for snackbars.
+class CaptureResult {
+  final String message;
+  final bool isError;
+  const CaptureResult(this.message, {this.isError = false});
+}
+
+/// The most recent capture result. UI watches this to show snackbars.
+/// Reset to null by the notifier before each new item so listeners always fire.
+final captureResultProvider = StateProvider<CaptureResult?>((_) => null);
+
+/// In-memory sequential work queue for quick captures.
+/// Separate from [captureQueueProvider] (which is the offline persistence queue).
+final captureWorkQueueProvider =
+    StateNotifierProvider<CaptureWorkQueueNotifier, List<String>>(
+  (ref) => CaptureWorkQueueNotifier(ref),
+);
+
+class CaptureWorkQueueNotifier extends StateNotifier<List<String>> {
+  final Ref _ref;
+  bool _running = false;
+
+  CaptureWorkQueueNotifier(this._ref) : super([]);
+
+  /// Add text to the queue and start the drain loop if not already running.
+  void enqueue(String text) {
+    state = [...state, text];
+    _drain();
+  }
+
+  Future<void> _drain() async {
+    if (_running) return;
+    _running = true;
+    try {
+      while (state.isNotEmpty) {
+        final text = state.first;
+        // Signal "no result yet" so the same result value can re-trigger watch.
+        _ref.read(captureResultProvider.notifier).state = null;
+        try {
+          final api = _ref.read(quickCaptureApiProvider);
+          final result = await api.capture(text);
+
+          // Dequeue on success.
+          state = state.length > 1 ? state.sublist(1) : [];
+
+          // Invalidate content providers so lists refresh.
+          switch (result.type) {
+            case 'note':
+              _ref.invalidate(notesProvider);
+            case 'task':
+            case 'todo':
+              _ref.invalidate(tasksProvider);
+          }
+
+          // Publish result for snackbar.
+          final msg = result.message.isNotEmpty
+              ? result.message
+              : '${_typeLabel(result.type)} created: ${result.title}';
+          _ref.read(captureResultProvider.notifier).state = CaptureResult(msg);
+        } on NetworkException catch (_) {
+          // Persist to offline queue and stop draining — still offline.
+          await _ref.read(captureQueueProvider.notifier).enqueue(text);
+          state = state.length > 1 ? state.sublist(1) : [];
+          _ref.read(captureResultProvider.notifier).state = CaptureResult(
+            "You're offline — capture saved and will retry automatically.",
+          );
+          break;
+        } on AppException catch (e) {
+          state = state.length > 1 ? state.sublist(1) : [];
+          _ref.read(captureResultProvider.notifier).state =
+              CaptureResult(e.message, isError: true);
+        } catch (_) {
+          state = state.length > 1 ? state.sublist(1) : [];
+          _ref.read(captureResultProvider.notifier).state =
+              CaptureResult('Capture failed. Please try again.', isError: true);
+        }
+      }
+    } finally {
+      _running = false;
+    }
+  }
+
+  String _typeLabel(String type) => switch (type) {
+        'note' => 'Note',
+        'task' => 'Task',
+        'event' => 'Event',
+        'todo' => 'To-do',
+        _ => type,
+      };
+}