Add multi-user authentication with JWT

- Users table with email/bcrypt-hashed password; register and login via /auth/ endpoints
- JWT tokens (30-day expiry) stored in localStorage; all API routes require Bearer auth
- All data (varieties, batches, settings, notification logs) scoped to the authenticated user
- Login/register screen overlays the app; sidebar shows user email and logout button
- Scheduler sends daily ntfy summaries for every configured user
- DB schema rewritten for multi-user; SECRET_KEY added to env

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/auth.py

@@ -0,0 +1,47 @@
+import os
+from datetime import datetime, timedelta
+
+import bcrypt
+from fastapi import Depends, HTTPException, status
+from fastapi.security import OAuth2PasswordBearer
+from jose import JWTError, jwt
+from sqlalchemy.orm import Session
+
+from database import get_db
+from models import User
+
+SECRET_KEY = os.environ.get("SECRET_KEY", "changeme-please-set-a-real-secret-in-env")
+ALGORITHM = "HS256"
+ACCESS_TOKEN_EXPIRE_DAYS = 30
+
+oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/auth/login")
+
+
+def verify_password(plain: str, hashed: str) -> bool:
+    return bcrypt.checkpw(plain.encode(), hashed.encode())
+
+
+def hash_password(password: str) -> str:
+    return bcrypt.hashpw(password.encode(), bcrypt.gensalt()).decode()
+
+
+def create_access_token(user_id: int) -> str:
+    expire = datetime.utcnow() + timedelta(days=ACCESS_TOKEN_EXPIRE_DAYS)
+    return jwt.encode({"sub": str(user_id), "exp": expire}, SECRET_KEY, algorithm=ALGORITHM)
+
+
+def get_current_user(token: str = Depends(oauth2_scheme), db: Session = Depends(get_db)) -> User:
+    exc = HTTPException(
+        status_code=status.HTTP_401_UNAUTHORIZED,
+        detail="Invalid or expired token",
+        headers={"WWW-Authenticate": "Bearer"},
+    )
+    try:
+        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
+        user_id = int(payload.get("sub"))
+    except (JWTError, TypeError, ValueError):
+        raise exc
+    user = db.query(User).filter(User.id == user_id).first()
+    if not user:
+        raise exc
+    return user