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>

pubspec.yaml

@@ -26,6 +26,18 @@ dev_dependencies:
   flutter_test:
     sdk: flutter
   flutter_lints: ^6.0.0
+  flutter_launcher_icons: ^0.14.3
+
+flutter_launcher_icons:
+  android: true
+  ios: false
+  remove_alpha_ios: false
+  image_path: "assets/icon/app_icon.png"
+  adaptive_icon_background: "#6366f1"
+  adaptive_icon_foreground: "assets/icon/app_icon_fg.png"
+  min_sdk_android: 21
 
 flutter:
   uses-material-design: true
+  assets:
+    - assets/icon/