fix: repair storage hot-path bugs and missing imports

- scripts.update_script: repoint script.current_object_id to the
  newly uploaded StorageObject and best-effort delete the old
  working copy. Previously the old row was mutated with the new
  content_hash while the script still pointed at it, silently
  losing user edits on the next publish_version.
- scripts.publish_version: read object bytes via the new
  RustFSObjectStore.get_bytes() instead of the non-existent
  .get_object(); publish 500'd on every call.
- scripts.upload_script / storage_api.complete_upload_record:
  Path(file_name) raised NameError (only PurePosixPath imported),
  crashing every upload and every upload finalization. Use
  PurePosixPath.
- RustFSObjectStore: add get_bytes() helper (sync, body.close in
  finally) for in-process callers that need raw bytes.

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

common/src/common/storage/rustfs.py

@@ -137,6 +137,14 @@ class RustFSObjectStore:
     def head(self, *, bucket_name: str, object_key: str) -> dict[str, Any]:
         return self.internal.head_object(Bucket=bucket_name, Key=object_key)
 
+    def get_bytes(self, *, bucket_name: str, object_key: str) -> bytes:
+        response = self.internal.get_object(Bucket=bucket_name, Key=object_key)
+        body: BinaryIO = response["Body"]
+        try:
+            return body.read()
+        finally:
+            body.close()
+
     def sha256(self, *, bucket_name: str, object_key: str) -> str:
         response = self.internal.get_object(Bucket=bucket_name, Key=object_key)
         body: BinaryIO = response["Body"]