feat(types): add custom type support to beads config (bd-649s)

Add types.custom config key mirroring the status.custom pattern:
- Add CustomTypeConfigKey constant and GetCustomTypes() to storage interface
- Add IssueType.IsValidWithCustom() method for validation
- Add ValidateWithCustom() to Issue for combined status/type validation
- Update all validation call sites to use GetCustomTypes()
- Rename parseCustomStatuses to parseCommaSeparated for reuse

This enables Gas Town to register custom types like agent/role/rig/convoy
without hardcoding them in beads core, supporting the type extraction epic.

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

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

Executed-By: beads/crew/dave
Rig: beads
Role: crew

internal/storage/sqlite/queries.go

@@ -75,11 +75,15 @@ func formatJSONStringArray(arr []string) string {
 
 // CreateIssue creates a new issue
 func (s *SQLiteStorage) CreateIssue(ctx context.Context, issue *types.Issue, actor string) error {
-	// Fetch custom statuses for validation
+	// Fetch custom statuses and types for validation
 	customStatuses, err := s.GetCustomStatuses(ctx)
 	if err != nil {
 		return fmt.Errorf("failed to get custom statuses: %w", err)
 	}
+	customTypes, err := s.GetCustomTypes(ctx)
+	if err != nil {
+		return fmt.Errorf("failed to get custom types: %w", err)
+	}
 
 	// Set timestamps first so defensive fixes can use them
 	now := time.Now()
@@ -111,8 +115,8 @@ func (s *SQLiteStorage) CreateIssue(ctx context.Context, issue *types.Issue, act
 		issue.DeletedAt = &deletedAt
 	}
 
-	// Validate issue before creating (with custom status support)
-	if err := issue.ValidateWithCustomStatuses(customStatuses); err != nil {
+	// Validate issue before creating (with custom status and type support)
+	if err := issue.ValidateWithCustom(customStatuses, customTypes); err != nil {
 		return fmt.Errorf("validation failed: %w", err)
 	}