Move JWT from localStorage to HttpOnly cookie; fix CSRF

- JWT stored in HttpOnly, Secure, SameSite=Strict cookie — JS cannot
  read the token at all; SameSite=Strict prevents CSRF without tokens
- Non-sensitive user payload returned in response body and stored in
  localStorage for UI purposes only (not usable for auth)
- Add POST /api/auth/logout endpoint that clears the cookie server-side
- Add SECURE_COOKIES env var (default true) for local HTTP testing
- Extract login.html inline script to login.js (CSP compliance)
- Remove Authorization: Bearer header from API calls; add credentials:
  include so cookies are sent automatically
- CSP script-src includes unsafe-inline to support existing onclick
  handlers throughout the app

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

backend/auth.py

@@ -4,8 +4,7 @@ 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 fastapi import Cookie, Depends, HTTPException, Response, status
 from sqlalchemy.orm import Session
 
 from database import get_db
@@ -14,9 +13,10 @@ from models import User
 SECRET_KEY = os.environ["JWT_SECRET"]
 ALGORITHM = "HS256"
 ACCESS_TOKEN_EXPIRE_DAYS = 30
+COOKIE_NAME = "token"
+SECURE_COOKIES = os.environ.get("SECURE_COOKIES", "true").lower() == "true"
 
 pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
-oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/api/auth/login")
 
 
 def verify_password(plain_password: str, hashed_password: str) -> bool:
@@ -41,28 +41,44 @@ def create_access_token(user_id: int, username: str, is_admin: bool, user_timezo
     return jwt.encode(payload, SECRET_KEY, algorithm=ALGORITHM)
 
 
-async def get_token_payload(
-    token: str = Depends(oauth2_scheme),
-) -> dict:
-    try:
-        return jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
-    except JWTError:
-        raise HTTPException(
-            status_code=status.HTTP_401_UNAUTHORIZED,
-            detail="Could not validate credentials",
-            headers={"WWW-Authenticate": "Bearer"},
-        )
+def set_auth_cookie(response: Response, token: str) -> None:
+    response.set_cookie(
+        key=COOKIE_NAME,
+        value=token,
+        httponly=True,
+        secure=SECURE_COOKIES,
+        samesite="strict",
+        max_age=ACCESS_TOKEN_EXPIRE_DAYS * 24 * 60 * 60,
+        path="/",
+    )
+
+
+def clear_auth_cookie(response: Response) -> None:
+    response.delete_cookie(key=COOKIE_NAME, httponly=True, secure=SECURE_COOKIES, samesite="strict", path="/")
+
+
+def token_to_user_payload(token: str) -> dict:
+    payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
+    return {
+        "sub":      payload["sub"],
+        "username": payload["username"],
+        "is_admin": payload["is_admin"],
+        "timezone": payload["timezone"],
+        "exp":      payload["exp"],
+        "admin_id": payload.get("admin_id"),
+    }
 
 
 async def get_current_user(
-    token: str = Depends(oauth2_scheme),
+    token: Optional[str] = Cookie(default=None, alias=COOKIE_NAME),
     db: Session = Depends(get_db),
 ) -> User:
     credentials_exception = HTTPException(
         status_code=status.HTTP_401_UNAUTHORIZED,
         detail="Could not validate credentials",
-        headers={"WWW-Authenticate": "Bearer"},
     )
+    if not token:
+        raise credentials_exception
     try:
         payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
         user_id_str: Optional[str] = payload.get("sub")
@@ -85,3 +101,20 @@ async def get_current_admin(current_user: User = Depends(get_current_user)) -> U
             detail="Admin access required",
         )
     return current_user
+
+
+async def get_token_payload(
+    token: Optional[str] = Cookie(default=None, alias=COOKIE_NAME),
+) -> dict:
+    if not token:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Could not validate credentials",
+        )
+    try:
+        return jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
+    except JWTError:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Could not validate credentials",
+        )