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/storage/sqlite/multirepo_export.go

@@ -54,7 +54,7 @@ func (s *SQLiteStorage) ExportToMultiRepo(ctx context.Context) (map[string]int,
 	// Wisps exist only in SQLite and are shared via .beads/redirect, not JSONL.
 	filtered := make([]*types.Issue, 0, len(allIssues))
 	for _, issue := range allIssues {
-		if !issue.Wisp {
+		if !issue.Ephemeral {
 			filtered = append(filtered, issue)
 		}
 	}