Add multi-user auth, admin panel, and timezone support; rename to Yolkbook

- Rename app from Eggtracker to Yolkbook throughout
- Add JWT-based authentication (python-jose, passlib/bcrypt)
- Add users table; all data tables gain user_id FK for full data isolation
- Super admin credentials sourced from ADMIN_USERNAME/ADMIN_PASSWORD env vars,
  synced on every startup; orphaned rows auto-assigned to admin post-migration
- Login page with self-registration; JWT stored in localStorage (30-day expiry)
- Admin panel (/admin): list users, reset passwords, disable/enable, delete,
  and impersonate (Login As) with Return to Admin banner
- Settings modal (gear icon in nav): timezone selector and change password
- Timezone stored per-user; stats date windows computed in user's timezone;
  date input setToday() respects user timezone via Intl API
- migrate_v2.sql for existing single-user installs
- Auto-migration adds timezone column to users on startup
- Updated README with full setup, auth, admin, and migration docs

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

backend/auth.py

@@ -0,0 +1,72 @@
+import os
+from datetime import datetime, timedelta, timezone
+from typing import Optional
+
+from jose import JWTError, jwt
+from passlib.context import CryptContext
+from fastapi import Depends, HTTPException, status
+from fastapi.security import OAuth2PasswordBearer
+from sqlalchemy.orm import Session
+
+from database import get_db
+from models import User
+
+SECRET_KEY = os.environ["JWT_SECRET"]
+ALGORITHM = "HS256"
+ACCESS_TOKEN_EXPIRE_DAYS = 30
+
+pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/api/auth/login")
+
+
+def verify_password(plain_password: str, hashed_password: str) -> bool:
+    return pwd_context.verify(plain_password, hashed_password)
+
+
+def hash_password(password: str) -> str:
+    return pwd_context.hash(password)
+
+
+def create_access_token(user_id: int, username: str, is_admin: bool, user_timezone: str = "UTC") -> str:
+    expire = datetime.now(timezone.utc) + timedelta(days=ACCESS_TOKEN_EXPIRE_DAYS)
+    payload = {
+        "sub": str(user_id),
+        "username": username,
+        "is_admin": is_admin,
+        "timezone": user_timezone,
+        "exp": expire,
+    }
+    return jwt.encode(payload, SECRET_KEY, algorithm=ALGORITHM)
+
+
+async def get_current_user(
+    token: str = Depends(oauth2_scheme),
+    db: Session = Depends(get_db),
+) -> User:
+    credentials_exception = HTTPException(
+        status_code=status.HTTP_401_UNAUTHORIZED,
+        detail="Could not validate credentials",
+        headers={"WWW-Authenticate": "Bearer"},
+    )
+    try:
+        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
+        user_id_str: Optional[str] = payload.get("sub")
+        if user_id_str is None:
+            raise credentials_exception
+        user_id = int(user_id_str)
+    except (JWTError, ValueError):
+        raise credentials_exception
+
+    user = db.get(User, user_id)
+    if user is None or user.is_disabled:
+        raise credentials_exception
+    return user
+
+
+async def get_current_admin(current_user: User = Depends(get_current_user)) -> User:
+    if not current_user.is_admin:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Admin access required",
+        )
+    return current_user