Add pin.go and unpin.go to cmd/bd/ for managing pinned issues. - bd pin <id> sets Pinned=true on an issue - bd unpin <id> sets Pinned=false on an issue Also adds Pinned field support to RPC UpdateArgs for daemon mode. 🤝 Slit 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>