fix(cookbook): use COOKBOOK_STATE_FILE constant for state path (#3623)

The module derived its state file path as Path(os.environ.get("DATA_DIR", "data"))
/ "cookbook_state.json". The correct env var is ODYSSEUS_DATA_DIR, which is
already read by src/constants.py and exported as COOKBOOK_STATE_FILE. When
ODYSSEUS_DATA_DIR is set (Docker, custom installs), the old code read the wrong
env var and silently wrote state to data/cookbook_state.json relative to CWD
while every other file resolved under the custom data directory.

Fixes #3621

routes/cookbook_routes.py

@@ -15,6 +15,7 @@ from pathlib import Path
 from fastapi import APIRouter, HTTPException, Request, Depends
 
 from src.auth_helpers import require_user
+from src.constants import COOKBOOK_STATE_FILE
 from pydantic import BaseModel
 
 from core.middleware import require_admin
@@ -54,7 +55,7 @@ _HF_TOKEN_STATUS_SNIPPET = (
 
 def setup_cookbook_routes() -> APIRouter:
     router = APIRouter(tags=["cookbook"])
-    _cookbook_state_path = Path(os.environ.get("DATA_DIR", "data")) / "cookbook_state.json"
+    _cookbook_state_path = Path(COOKBOOK_STATE_FILE)
 
     def _mask_secret(value: str) -> str:
         if not value: