Fix bugs across app + server, optimize UI/UX, add Gitea CI

Bug fixes (Flutter):
- Wrap multi-statement DB writes (insert/update/delete note, deleteDocument,
  deletePageData, OCR FTS merge, migrations) in transactions to prevent data
  loss on interruption and a read-modify-write FTS race.
- Fix PdfDocument leaks on exception (try/finally dispose) and preserve image
  aspect ratio when stamping images onto PDF pages.
- Guard file-picker against empty selection (was .single -> crash).
- Fix eraser ConcurrentModificationError and unmodifiable-list crash on PDF
  pages; capture page synchronously on save to stop wrong-page data loss.
- Fix Riverpod DB-not-ready races, broken pull-to-refresh, settings load race,
  and search N+1; transform stored annotations on PDF page rotation.
- Normalize pen pressure for devices without a pressure range.
- PPT: single source of truth for slide strokes so ink displays and exports.

UI/UX:
- Material 3 typography, theme-aware colors (dark-mode fixes), hover cursors
  and right-click/visible actions on desktop, keyboard shortcuts (undo/redo/
  save/find), toolbar overflow handling, friendlier empty states, semantic OCR
  status badges, relative timestamps, 1-based page indicators, large-deck PPT
  navigation, and a scratchpad-scope label in split view.

Server (optional backend):
- Persist JWT secret (was per-process random), block path traversal in storage,
  fix CORS '*'+credentials, add OCR job ownership checks, last-writer-wins sync
  guard, constant-time login, and split out heavy OCR deps so the API/tests run
  without them.

CI: Gitea workflows for format+analyze+test (Linux, system sqlite) and a
Windows release build; pristine `flutter analyze`, all Flutter and server tests
green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/providers/settings_provider.dart

@@ -0,0 +1,146 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+import '../models/pen_tool.dart';
+import '../models/pressure_curve.dart';
+import '../utils/stroke_stabilizer.dart';
+
+final settingsProvider = ChangeNotifierProvider<SettingsNotifier>(
+  (ref) => SettingsNotifier(),
+);
+
+/// Persists user settings across sessions using SharedPreferences.
+class SettingsNotifier extends ChangeNotifier {
+  late SharedPreferences _prefs;
+
+  /// Completes once [_load] has assigned [_prefs]. Setters await this before
+  /// touching [_prefs] to avoid a LateInitializationError when invoked before
+  /// the fire-and-forget load from the constructor finishes.
+  late final Future<void> _ready;
+
+  PenTool _defaultTool = PenTool.pen;
+  Color _defaultColor = Colors.black;
+  double _defaultStrokeWidth = 2.0;
+  PressureCurveType _defaultPressureCurve = PressureCurveType.linear;
+  StabilizationLevel _defaultStabilization = StabilizationLevel.none;
+  ThemeMode _themeMode = ThemeMode.system;
+  Color _colorSchemeSeed = Colors.blue;
+
+  SettingsNotifier() {
+    _ready = _load();
+  }
+
+  PenTool get defaultTool => _defaultTool;
+  Color get defaultColor => _defaultColor;
+  double get defaultStrokeWidth => _defaultStrokeWidth;
+  PressureCurveType get defaultPressureCurve => _defaultPressureCurve;
+  StabilizationLevel get defaultStabilization => _defaultStabilization;
+  ThemeMode get themeMode => _themeMode;
+  Color get colorSchemeSeed => _colorSchemeSeed;
+
+  Future<void> setDefaultTool(PenTool tool) async {
+    _defaultTool = tool;
+    notifyListeners();
+    await _ready;
+    await _prefs.setString('defaultTool', tool.name);
+  }
+
+  Future<void> setDefaultColor(Color color) async {
+    _defaultColor = color;
+    notifyListeners();
+    await _ready;
+    await _prefs.setInt('defaultColor', color.toARGB32());
+  }
+
+  Future<void> setDefaultStrokeWidth(double width) async {
+    _defaultStrokeWidth = width;
+    notifyListeners();
+    await _ready;
+    await _prefs.setDouble('defaultStrokeWidth', width);
+  }
+
+  Future<void> setDefaultPressureCurve(PressureCurveType curve) async {
+    _defaultPressureCurve = curve;
+    notifyListeners();
+    await _ready;
+    await _prefs.setString('defaultPressureCurve', curve.name);
+  }
+
+  Future<void> setDefaultStabilization(StabilizationLevel level) async {
+    _defaultStabilization = level;
+    notifyListeners();
+    await _ready;
+    await _prefs.setString('defaultStabilization', level.name);
+  }
+
+  Future<void> setThemeMode(ThemeMode mode) async {
+    _themeMode = mode;
+    notifyListeners();
+    await _ready;
+    await _prefs.setString('themeMode', mode.name);
+  }
+
+  Future<void> setColorSchemeSeed(Color color) async {
+    _colorSchemeSeed = color;
+    notifyListeners();
+    await _ready;
+    await _prefs.setInt('colorSchemeSeed', color.toARGB32());
+  }
+
+  Future<void> clearAllData() async {
+    await _ready;
+    await _prefs.clear();
+    _defaultTool = PenTool.pen;
+    _defaultColor = Colors.black;
+    _defaultStrokeWidth = 2.0;
+    _defaultPressureCurve = PressureCurveType.linear;
+    _defaultStabilization = StabilizationLevel.none;
+    _themeMode = ThemeMode.system;
+    _colorSchemeSeed = Colors.blue;
+    notifyListeners();
+  }
+
+  Future<void> _load() async {
+    _prefs = await SharedPreferences.getInstance();
+
+    final toolName = _prefs.getString('defaultTool');
+    if (toolName != null) {
+      _defaultTool = PenTool.values.asNameMap()[toolName] ?? PenTool.pen;
+    }
+
+    final colorValue = _prefs.getInt('defaultColor');
+    if (colorValue != null) {
+      _defaultColor = Color(colorValue);
+    }
+
+    _defaultStrokeWidth =
+        _prefs.getDouble('defaultStrokeWidth') ?? _defaultStrokeWidth;
+
+    final curveName = _prefs.getString('defaultPressureCurve');
+    if (curveName != null) {
+      _defaultPressureCurve =
+          PressureCurveType.values.asNameMap()[curveName] ??
+          PressureCurveType.linear;
+    }
+
+    final stabName = _prefs.getString('defaultStabilization');
+    if (stabName != null) {
+      _defaultStabilization =
+          StabilizationLevel.values.asNameMap()[stabName] ??
+          StabilizationLevel.none;
+    }
+
+    final themeName = _prefs.getString('themeMode');
+    if (themeName != null) {
+      _themeMode = ThemeMode.values.asNameMap()[themeName] ?? ThemeMode.system;
+    }
+
+    final seedValue = _prefs.getInt('colorSchemeSeed');
+    if (seedValue != null) {
+      _colorSchemeSeed = Color(seedValue);
+    }
+
+    notifyListeners();
+  }
+}