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/services/pen_input_service.dart

@@ -0,0 +1,62 @@
+import 'dart:async';
+
+import 'package:flutter/gestures.dart';
+import 'package:flutter/material.dart';
+
+import '../models/ink_point.dart';
+import '../models/pen_tool.dart';
+import '../models/pointer_device_kind.dart';
+
+class PenInputService {
+  final StreamController<InkPoint> _pointController =
+      StreamController<InkPoint>.broadcast();
+
+  Stream<InkPoint> get pointStream => _pointController.stream;
+
+  PenTool currentTool = PenTool.pen;
+  Color currentColor = Colors.black;
+  double currentStrokeWidth = 2.0;
+
+  void addPoint(InkPoint point) {
+    _pointController.add(point);
+  }
+
+  InputDeviceKind mapFlutterKind(PointerDeviceKind kind) {
+    switch (kind) {
+      case PointerDeviceKind.touch:
+        return InputDeviceKind.touch;
+      case PointerDeviceKind.mouse:
+        return InputDeviceKind.mouse;
+      case PointerDeviceKind.stylus:
+        return InputDeviceKind.stylus;
+      case PointerDeviceKind.invertedStylus:
+        return InputDeviceKind.invertedStylus;
+      case PointerDeviceKind.trackpad:
+        return InputDeviceKind.trackpad;
+      case PointerDeviceKind.unknown:
+        return InputDeviceKind.unknown;
+    }
+  }
+
+  InkPoint fromPointerEvent(PointerEvent event) {
+    // Devices without real pressure support (mouse, basic touch) report a
+    // degenerate range where pressureMin == pressureMax, which can yield a
+    // pressure of 0.0 and produce zero-width strokes. In that case fall back
+    // to a neutral mid-pressure value so strokes remain visible.
+    final pressure = event.pressureMin == event.pressureMax
+        ? 0.5
+        : event.pressure;
+    return InkPoint(
+      x: event.localPosition.dx,
+      y: event.localPosition.dy,
+      pressure: pressure,
+      tilt: event is PointerMoveEvent ? event.tilt : 0.0,
+      timestamp: event.timeStamp.inMicroseconds,
+      pointerDeviceKind: mapFlutterKind(event.kind),
+    );
+  }
+
+  void dispose() {
+    _pointController.close();
+  }
+}