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/badnote_server/main.py

@@ -0,0 +1,55 @@
+"""BadNote FastAPI server — main application."""
+
+import os
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from .config import settings
+from .database import close_db, init_db
+from .routers.auth_router import router as auth_router
+from .routers.notes_router import router as notes_router
+from .routers.documents_router import router as documents_router
+from .routers.ocr_router import router as ocr_router
+from .routers.sync_router import router as sync_router
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """Startup: create directories and init DB. Shutdown: close DB."""
+    os.makedirs(settings.storage_path, exist_ok=True)
+    for subdir in ("pending", "processing", "done", "failed"):
+        os.makedirs(os.path.join(settings.queue_path, subdir), exist_ok=True)
+    await init_db()
+    yield
+    await close_db()
+
+
+app = FastAPI(title="BadNote Server", version="1.0.0", lifespan=lifespan)
+
+# Authentication is Bearer-token based, so cookies/credentials are not needed.
+# `allow_origins=["*"]` together with `allow_credentials=True` is an invalid and
+# insecure combination, so we keep credentials disabled. Set BADNOTE_CORS_ORIGINS
+# (comma-separated) to lock the API down to specific front-end origins.
+_cors_origins = settings.cors_origins or ["*"]
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=_cors_origins,
+    allow_credentials=False,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+app.include_router(auth_router, prefix="/api/auth", tags=["auth"])
+app.include_router(notes_router, prefix="/api/notes", tags=["notes"])
+app.include_router(documents_router, prefix="/api/documents", tags=["documents"])
+app.include_router(ocr_router, prefix="/api/ocr", tags=["ocr"])
+app.include_router(sync_router, prefix="/api/sync", tags=["sync"])
+
+
+@app.get("/api/ping")
+async def ping() -> dict:
+    """Health check endpoint."""
+    return {"status": "ok"}