fix(pin): add 'pinned' field to allowed update fields (gt-zr0a)

The 'bd pin' command was failing with "invalid field for update: pinned"
because the pinned field was missing from allowedUpdateFields.

Fixes:
- Add 'pinned' to allowedUpdateFields in queries.go
- Update importer to include pinned field in updates during import
- Add equalBool comparator for IssueDataChanged to detect pinned changes
- Fix stats query to count pinned=1 instead of status='pinned'
- Fix pinIndicator in list.go to check issue.Pinned instead of status

This unblocks gt mail --pinned functionality.

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

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

cmd/bd/list.go

@@ -38,9 +38,9 @@ func parseTimeFlag(s string) (time.Time, error) {
 	return time.Time{}, fmt.Errorf("unable to parse time %q (try formats: 2006-01-02, 2006-01-02T15:04:05, or RFC3339)", s)
 }
 
-// pinIndicator returns a pushpin emoji prefix for pinned issues (bd-18b)
+// pinIndicator returns a pushpin emoji prefix for pinned issues (bd-18b, bd-7h5)
 func pinIndicator(issue *types.Issue) string {
-	if issue.Status == types.StatusPinned {
+	if issue.Pinned {
 		return "📌 "
 	}
 	return ""