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/document.g.dart

@@ -0,0 +1,31 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'document.dart';
+
+// **************************************************************************
+// JsonSerializableGenerator
+// **************************************************************************
+
+_$DocumentImpl _$$DocumentImplFromJson(Map<String, dynamic> json) =>
+    _$DocumentImpl(
+      id: json['id'] as String,
+      filename: json['filename'] as String,
+      docType: json['docType'] as String,
+      filePath: json['filePath'] as String,
+      pageCount: (json['pageCount'] as num?)?.toInt() ?? 0,
+      rotation: (json['rotation'] as num?)?.toInt() ?? 0,
+      createdAt: DateTime.parse(json['createdAt'] as String),
+      updatedAt: DateTime.parse(json['updatedAt'] as String),
+    );
+
+Map<String, dynamic> _$$DocumentImplToJson(_$DocumentImpl instance) =>
+    <String, dynamic>{
+      'id': instance.id,
+      'filename': instance.filename,
+      'docType': instance.docType,
+      'filePath': instance.filePath,
+      'pageCount': instance.pageCount,
+      'rotation': instance.rotation,
+      'createdAt': instance.createdAt.toIso8601String(),
+      'updatedAt': instance.updatedAt.toIso8601String(),
+    };