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/auth.py

@@ -0,0 +1,73 @@
+"""JWT authentication utilities for BadNote."""
+
+from datetime import datetime, timedelta, timezone
+from uuid import uuid4
+
+from fastapi import Depends, HTTPException, status
+from fastapi.security import HTTPAuthorizationCredentials, HTTPBearer
+from jose import JWTError, jwt
+from passlib.context import CryptContext
+
+from .config import settings
+
+pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+bearer_scheme = HTTPBearer()
+
+
+def hash_password(password: str) -> str:
+    """Hash a plaintext password with bcrypt."""
+    return pwd_context.hash(password)
+
+
+def verify_password(password: str, password_hash: str) -> bool:
+    """Verify a password against its hash."""
+    return pwd_context.verify(password, password_hash)
+
+
+# A precomputed hash used to spend roughly the same time verifying a password
+# for a non-existent user as for an existing one, so login response timing does
+# not leak whether a username exists.
+_DUMMY_HASH = pwd_context.hash("badnote-dummy-password")
+
+
+def dummy_verify() -> None:
+    """Run a throwaway bcrypt verification to equalise login timing."""
+    pwd_context.verify("badnote-dummy-password", _DUMMY_HASH)
+
+
+def create_access_token(user_id: str) -> str:
+    """Create a JWT access token for the given user_id."""
+    expire = datetime.now(timezone.utc) + timedelta(hours=settings.jwt_expiry_hours)
+    payload = {
+        "sub": user_id,
+        "exp": expire,
+        "iat": datetime.now(timezone.utc),
+        "jti": str(uuid4()),
+    }
+    return jwt.encode(payload, settings.jwt_secret, algorithm="HS256")
+
+
+def decode_access_token(token: str) -> dict:
+    """Decode and validate a JWT token. Returns the payload dict."""
+    try:
+        payload = jwt.decode(token, settings.jwt_secret, algorithms=["HS256"])
+        return payload
+    except JWTError as exc:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Invalid or expired token",
+        ) from exc
+
+
+async def get_current_user(
+    credentials: HTTPAuthorizationCredentials = Depends(bearer_scheme),
+) -> str:
+    """FastAPI dependency: extract user_id from Bearer token."""
+    payload = decode_access_token(credentials.credentials)
+    user_id: str | None = payload.get("sub")
+    if user_id is None:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Token missing subject",
+        )
+    return user_id