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/sync_export.go

@@ -65,7 +65,7 @@ func exportToJSONL(ctx context.Context, jsonlPath string) error {
 	// This prevents "zombie" issues that resurrect after mol squash deletes them.
 	filteredIssues := make([]*types.Issue, 0, len(issues))
 	for _, issue := range issues {
-		if issue.Wisp {
+		if issue.Ephemeral {
 			continue
 		}
 		filteredIssues = append(filteredIssues, issue)