Add signed Studio identity setting

app/core/config.py

@@ -49,6 +49,8 @@ class Settings(BaseSettings):
     ffmpeg_binary: str = "ffmpeg"
     ffprobe_binary: str = "ffprobe"
     auth_enabled: bool = True
+    # Shared HMAC secret for verified Supabase identities forwarded by Studio's server proxy.
+    studio_identity_secret: SecretStr | None = None
     database_url: str = "sqlite+aiosqlite:///./data/mediarouter.db"
     # Security/tenant tables are created from ORM metadata at startup when missing.
     # SQL migrations remain required for PostgreSQL-specific RLS policies and constraints.