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>

cmd/bd/version.go

@@ -14,7 +14,7 @@ import (
 
 var (
 	// Version is the current version of bd (overridden by ldflags at build time)
-	Version = "0.36.0"
+	Version = "0.38.0"
 	// Build can be set via ldflags at compile time
 	Build = "dev"
 	// Commit and branch the git revision the binary was built from (optional ldflag)