chore(claude): add onboard config — memory, tasks, audit, gitignore

Onboard scaffolding for the dotfiles repo: 5 memory registries,
TODO backlog, onboard audit report, and .gitignore (ignores
Oldconfig, vim swap, .claude/settings.local.json).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,17 @@
+# OS junk
+.DS_Store
+Thumbs.db
+
+# Vim swap / backup
+*.swp
+*.swo
+*~
+
+# Local install backup (created by install.sh)
+Oldconfig/
+
+# onboard audit raw outputs (consumed by /onboard STEP 7)
+.onboard-audit/
+
+# Claude local settings (machine-specific)
+.claude/settings.local.json