fix: correggi path static dir (parent.parent invece di parent.parent.parent)

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

backend/app/main.py

@@ -150,7 +150,7 @@ def health():
 # SPA catch-all mount (MUST be last)
 # ---------------------------------------------------------------------------
 
-_STATIC_DIR = Path(__file__).parent.parent.parent / "static"
+_STATIC_DIR = Path(__file__).parent.parent / "static"
 
 if _STATIC_DIR.exists():
     app.mount("/", SPAStaticFiles(directory=str(_STATIC_DIR), html=True), name="spa")