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>

server/tests/test_auth.py

@@ -0,0 +1,82 @@
+"""Tests for auth endpoints."""
+
+import sys, os
+sys.path.insert(0, os.path.dirname(__file__))
+
+import pytest
+import pytest_asyncio
+from httpx import AsyncClient
+from helpers import auth_header, register_and_login
+
+
+@pytest.mark.asyncio
+async def test_register(client: AsyncClient):
+    resp = await client.post(
+        "/api/auth/register",
+        json={"username": "newuser", "password": "password123"},
+    )
+    assert resp.status_code == 201
+    data = resp.json()
+    assert "token" in data
+    assert "user_id" in data
+
+
+@pytest.mark.asyncio
+async def test_register_duplicate(client: AsyncClient):
+    await client.post(
+        "/api/auth/register",
+        json={"username": "dupuser", "password": "password123"},
+    )
+    resp = await client.post(
+        "/api/auth/register",
+        json={"username": "dupuser", "password": "password123"},
+    )
+    assert resp.status_code == 409
+
+
+@pytest.mark.asyncio
+async def test_login(client: AsyncClient):
+    await client.post(
+        "/api/auth/register",
+        json={"username": "loginuser", "password": "mypassword"},
+    )
+    resp = await client.post(
+        "/api/auth/login",
+        json={"username": "loginuser", "password": "mypassword"},
+    )
+    assert resp.status_code == 200
+    data = resp.json()
+    assert "token" in data
+    assert "user_id" in data
+
+
+@pytest.mark.asyncio
+async def test_login_wrong_password(client: AsyncClient):
+    await client.post(
+        "/api/auth/register",
+        json={"username": "wrongpw", "password": "correct"},
+    )
+    resp = await client.post(
+        "/api/auth/login",
+        json={"username": "wrongpw", "password": "incorrect"},
+    )
+    assert resp.status_code == 401
+
+
+@pytest.mark.asyncio
+async def test_refresh(client: AsyncClient):
+    token, user_id = await register_and_login(client)
+    resp = await client.post(
+        "/api/auth/refresh",
+        headers=auth_header(token),
+    )
+    assert resp.status_code == 200
+    data = resp.json()
+    assert "token" in data
+    assert data["user_id"] == user_id
+
+
+@pytest.mark.asyncio
+async def test_refresh_no_token(client: AsyncClient):
+    resp = await client.post("/api/auth/refresh")
+    assert resp.status_code in (401, 403)