fix(gitea): guard against empty response in ListContents fallback

Add defensive check for empty Name and Path fields when unmarshaling
a single ContentEntry in the fallback path. While Gitea API won't
return empty objects for valid file paths, this guard:
- Explicitly documents the invariant we expect
- Catches potential API behavior changes early
- Costs nothing at runtime

Addresses [MINOR] from sonnet-review-bot on PR #74.

gitea/client.go

@@ -458,6 +458,10 @@ func (c *Client) ListContents(ctx context.Context, owner, repo, path string) ([]
 		if err2 := json.Unmarshal(body, &single); err2 != nil {
 			return nil, fmt.Errorf("parse contents JSON: %w", err)
 		}
+		// Guard against empty/malformed responses
+		if single.Name == "" && single.Path == "" {
+			return nil, fmt.Errorf("parse contents JSON: empty response for path %q", path)
+		}
 		entries = []ContentEntry{single}
 	}
 	return entries, nil