fix: atomicWriteFile falls back to direct write on bind mounts

Rename fails with EBUSY on Docker bind-mounted files (e.g. controller.yaml).
Fall back to os.WriteFile when os.Rename fails.

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

controller/internal/setup/handlers.go

@@ -1032,7 +1032,8 @@ func atomicWriteFile(path string, data []byte, perm os.FileMode) error {
 	}
 	if err := os.Rename(tmp, path); err != nil {
 		os.Remove(tmp)
-		return err
+		// Rename fails on bind-mounted files (EBUSY). Fall back to direct write.
+		return os.WriteFile(path, data, perm)
 	}
 	return nil
 }