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>

.gitea/workflows/windows-build.yml

@@ -0,0 +1,57 @@
+name: Windows Build
+
+on:
+  push:
+    branches: [main]
+    tags: ["v*"]
+  pull_request:
+    branches: [main]
+  workflow_dispatch:
+
+env:
+  FLUTTER_VERSION: "3.41.4"
+
+jobs:
+  build-windows:
+    name: Build Windows (x64)
+    runs-on: windows-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Flutter
+        uses: subosito/flutter-action@v2
+        with:
+          flutter-version: ${{ env.FLUTTER_VERSION }}
+          channel: stable
+          cache: true
+
+      - name: Enable Windows desktop
+        run: flutter config --enable-windows-desktop
+
+      - name: Install dependencies
+        run: flutter pub get
+
+      - name: Analyze
+        run: flutter analyze
+
+      # The sqlite3 native asset downloads a precompiled DLL from GitHub
+      # releases. If the runner is behind a firewall, set HTTP_PROXY /
+      # HTTPS_PROXY as repository secrets and they will be honoured here.
+      - name: Build Windows release
+        env:
+          HTTP_PROXY: ${{ secrets.HTTP_PROXY }}
+          HTTPS_PROXY: ${{ secrets.HTTPS_PROXY }}
+        run: flutter build windows --release
+
+      - name: Package artifact
+        run: |
+          $dir = "build\windows\x64\runner\Release"
+          Compress-Archive -Path "$dir\*" -DestinationPath "badnote-windows-x64.zip" -Force
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: badnote-windows-x64
+          path: badnote-windows-x64.zip
+          if-no-files-found: error