fix(storage): allow S3 without public_url, auto-construct path-style URL from endpoint

app/storage.py

@@ -120,7 +120,9 @@ class S3Storage:
         k = _strip_prefix(key)
         if self.public_url:
             return f"{self.public_url}/{k}"
-        return k
+        # fallback: path-style URL from endpoint + bucket
+        ep = self._client._endpoint.host
+        return f"{ep}/{self.bucket}/{k}"
 
 
 # ── Helpers ────────────────────────────────────────────────────────