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/models/ink_point.g.dart

@@ -0,0 +1,42 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'ink_point.dart';
+
+// **************************************************************************
+// JsonSerializableGenerator
+// **************************************************************************
+
+_$InkPointImpl _$$InkPointImplFromJson(Map<String, dynamic> json) =>
+    _$InkPointImpl(
+      x: (json['x'] as num).toDouble(),
+      y: (json['y'] as num).toDouble(),
+      pressure: (json['pressure'] as num?)?.toDouble() ?? 0.5,
+      tilt: (json['tilt'] as num?)?.toDouble() ?? 0.0,
+      timestamp: (json['timestamp'] as num).toInt(),
+      pointerDeviceKind:
+          $enumDecodeNullable(
+            _$InputDeviceKindEnumMap,
+            json['pointerDeviceKind'],
+          ) ??
+          InputDeviceKind.unknown,
+    );
+
+Map<String, dynamic> _$$InkPointImplToJson(
+  _$InkPointImpl instance,
+) => <String, dynamic>{
+  'x': instance.x,
+  'y': instance.y,
+  'pressure': instance.pressure,
+  'tilt': instance.tilt,
+  'timestamp': instance.timestamp,
+  'pointerDeviceKind': _$InputDeviceKindEnumMap[instance.pointerDeviceKind]!,
+};
+
+const _$InputDeviceKindEnumMap = {
+  InputDeviceKind.touch: 'touch',
+  InputDeviceKind.mouse: 'mouse',
+  InputDeviceKind.stylus: 'stylus',
+  InputDeviceKind.invertedStylus: 'invertedStylus',
+  InputDeviceKind.trackpad: 'trackpad',
+  InputDeviceKind.unknown: 'unknown',
+};