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>

internal/rpc/server_routing_validation_diagnostics.go

@@ -188,6 +188,8 @@ func (s *Server) handleRequest(req *Request) Response {
 		resp = s.handleResolveID(req)
 	case OpReady:
 		resp = s.handleReady(req)
+	case OpBlocked:
+		resp = s.handleBlocked(req)
 	case OpStale:
 		resp = s.handleStale(req)
 	case OpStats: