refactor: remove unused bd pin/unpin/hook commands (bd-x0zl)

Analysis found these commands are dead code:
- gt never calls `bd pin` - uses `bd update --status=pinned` instead
- Beads.Pin() wrapper exists but is never called
- bd hook functionality duplicated by gt mol status
- Code comment says "pinned field is cosmetic for bd hook visibility"

Removed:
- cmd/bd/pin.go
- cmd/bd/unpin.go
- cmd/bd/hook.go

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/DELETIONS.md

@@ -202,7 +202,7 @@ The 1-hour grace period ensures tombstones propagate even with minor clock drift
 
 ## Wisps: Intentional Tombstone Bypass
 
-**Wisps** (ephemeral issues created by `bd wisp create`) are intentionally excluded from tombstone tracking.
+**Wisps** (ephemeral issues created by `bd mol wisp`) are intentionally excluded from tombstone tracking.
 
 ### Why Wisps Don't Need Tombstones