chore: update .gitignore to include .private directory

- Added `.private/` to .gitignore for root-level private documentation
- Complements existing `docs/.private/` pattern
- Cleaned up 2.3GB of build artifacts (node_modules, dist, target, .venv)
- Improves repository hygiene and git performance

Author: NormB

.gitignore

@@ -36,6 +36,7 @@ logs/
 
 # Private documentation (WIP files, task tracking, test results)
 docs/.private/
+.private/
 
 # Work directory (temporary files, scan results, development artifacts)
 work/