docs: move archive to ~/.doc-archive, ignore doc/archive/

- Move old docs to ~/.localpibox/.doc-archive/ (outside repo)
- Add doc/archive/ to .gitignore
- Remove backup_repos.py (moved to workspace root)
- Clean test file from backup references
- Ready for fresh, consistent documentation generation

Author: cfxdevkit

.gitignore

@@ -3,3 +3,5 @@
 # NOT tracked in git. Recreated by:
 #   ./support/version.sh workspace sync
 /workspace
+# ── Documentation archive (moved, not regenerated yet) ─────────────────────
+doc/archive/