feat(types): add "enhancement" as alias for "feature" type

Support --type enhancement as an alias for --type feature when creating
issues. The normalization happens before validation to ensure consistency
across all code paths.

Closes gt-hzanoe

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

internal/storage/sqlite/validators.go

@@ -40,7 +40,8 @@ func validateStatusWithCustom(value interface{}, customStatuses []string) error
 // validateIssueType validates an issue type value
 func validateIssueType(value interface{}) error {
 	if issueType, ok := value.(string); ok {
-		if !types.IssueType(issueType).IsValid() {
+		// Normalize first to support aliases like "enhancement" -> "feature"
+		if !types.IssueType(issueType).Normalize().IsValid() {
 			return fmt.Errorf("invalid issue type: %s", issueType)
 		}
 	}