fix hugging face cache issues

.gitignore

@@ -3,6 +3,7 @@
 /__pycache__
 __pycache__
 /data2
+/.cache
 # /physical_db/physical_database.csv
 # /physical_db
 

panel_app/panel_v2_backend.py

@@ -10,8 +10,17 @@ def _project_root() -> str:
 
 
 def cache_root() -> str:
-    root = _project_root()
-    path = os.path.join(root, ".cache", "panel_app_v2")
+    # Priority: env var > /tmp (for HF Spaces/containers) > project root (local dev)
+    env_cache = os.environ.get("CACHE_DIR")
+    if env_cache:
+        path = os.path.join(env_cache, "panel_app_v2")
+    elif os.path.exists("/tmp") and os.access("/tmp", os.W_OK):
+        # On Hugging Face Spaces and Linux containers, /tmp is always writable
+        path = os.path.join("/tmp", "panel_app_v2_cache")
+    else:
+        # Fallback to project root for local development
+        root = _project_root()
+        path = os.path.join(root, ".cache", "panel_app_v2")
     os.makedirs(path, exist_ok=True)
     return path