* fix: narrow bare except Exception in VS Code settings merge
Replace overly broad except Exception with (OSError, ValueError, KeyError)
to let programming errors like TypeError or AttributeError propagate while
still handling expected I/O and parse errors gracefully.
* test: verify programming errors propagate through handle_vscode_settings
The narrow exception change from 'except Exception' to
'except (OSError, ValueError, KeyError)' was not covered by a
regression test. Add a test that monkeypatches merge_json_files to
raise TypeError and verifies it propagates rather than being swallowed.
