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>

test/undo_manager_test.dart

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+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:badnote/models/ink_point.dart';
+import 'package:badnote/models/ink_stroke.dart';
+import 'package:badnote/models/pen_tool.dart';
+import 'package:badnote/services/undo_manager.dart';
+
+InkStroke _stroke(String id) => InkStroke(
+  id: id,
+  points: const [
+    InkPoint(x: 0, y: 0, pressure: 0.5, tilt: 0, timestamp: 0),
+    InkPoint(x: 1, y: 1, pressure: 0.5, tilt: 0, timestamp: 1),
+  ],
+  tool: PenTool.pen,
+  createdAt: DateTime(2024, 1, 1),
+);
+
+void main() {
+  group('UndoManager', () {
+    test('starts empty with no undo/redo available', () {
+      final m = UndoManager();
+      expect(m.currentStrokes, isEmpty);
+      expect(m.canUndo, isFalse);
+      expect(m.canRedo, isFalse);
+    });
+
+    test('addStroke then undo/redo round-trips the stroke', () {
+      final m = UndoManager();
+      final s = _stroke('a');
+
+      m.addStroke(s);
+      expect(m.currentStrokes.map((e) => e.id), ['a']);
+      expect(m.canUndo, isTrue);
+
+      m.undo();
+      expect(m.currentStrokes, isEmpty);
+      expect(m.canRedo, isTrue);
+
+      m.redo();
+      expect(m.currentStrokes.map((e) => e.id), ['a']);
+    });
+
+    test('a new stroke clears the redo stack', () {
+      final m = UndoManager();
+      m.addStroke(_stroke('a'));
+      m.undo();
+      expect(m.canRedo, isTrue);
+
+      m.addStroke(_stroke('b'));
+      expect(m.canRedo, isFalse);
+      expect(m.currentStrokes.map((e) => e.id), ['b']);
+    });
+
+    test('removeStroke with replacements (partial erase) is reversible', () {
+      final m = UndoManager();
+      m.addStroke(_stroke('whole'));
+
+      m.removeStroke(
+        _stroke('whole'),
+        replacements: [_stroke('part1'), _stroke('part2')],
+      );
+      expect(m.currentStrokes.map((e) => e.id), ['part1', 'part2']);
+
+      // Undo restores the original and drops the replacements.
+      m.undo();
+      expect(m.currentStrokes.map((e) => e.id), ['whole']);
+
+      // Redo re-applies the erase.
+      m.redo();
+      expect(m.currentStrokes.map((e) => e.id), ['part1', 'part2']);
+    });
+
+    test('currentStrokes is an unmodifiable view', () {
+      final m = UndoManager();
+      m.addStroke(_stroke('a'));
+      expect(() => m.currentStrokes.add(_stroke('b')), throwsUnsupportedError);
+    });
+  });
+}

test/widget_test.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+import 'package:badnote/screens/home_screen.dart';
+
+void main() {
+  testWidgets('Home screen renders its app bar title', (
+    WidgetTester tester,
+  ) async {
+    // The note list is backed by the on-device database, which is not
+    // available in the widget-test environment; the body therefore shows a
+    // loading/error state. The app-bar chrome renders regardless, so we assert
+    // on that. The home screen must be wrapped in a ProviderScope, which the
+    // app's real entrypoint (main.dart) provides.
+    SharedPreferences.setMockInitialValues({});
+
+    await tester.pumpWidget(
+      const ProviderScope(child: MaterialApp(home: HomeScreen())),
+    );
+    await tester.pump();
+
+    expect(find.text('BadNote'), findsOneWidget);
+    expect(find.byTooltip('Search'), findsOneWidget);
+  });
+}