Fix ox-hugo export with internal ID links and Quartz config

- Add org-id resolution for [[id:...]] links by building ID locations
  database once before parallel export
- Handle broken file links gracefully with org-export-with-broken-links
- Fix race condition in parallel exports by pre-building ID cache
- Fix Quartz config not being applied: cp was preserving nix store hash
  prefix in filename instead of using explicit destination filename
- Continue pipeline even when some exports fail, reporting failures
- Improve error handling and logging throughout export pipeline

.gitignore

@@ -25,3 +25,4 @@ dist/
 # This repo - generated output
 content/
 static/
+.agent-shell/