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)
 		}
 	}

internal/types/types.go

@@ -528,6 +528,17 @@ func (t IssueType) IsValidWithCustom(customTypes []string) bool {
 	return false
 }
 
+// Normalize maps issue type aliases to their canonical form.
+// For example, "enhancement" -> "feature".
+func (t IssueType) Normalize() IssueType {
+	switch t {
+	case "enhancement":
+		return TypeFeature
+	default:
+		return t
+	}
+}
+
 // RequiredSection describes a recommended section for an issue type.
 // Used by bd lint and bd create --validate for template validation.
 type RequiredSection struct {

internal/validation/bead.go

@@ -28,8 +28,10 @@ func ParsePriority(content string) int {
 
 // ParseIssueType extracts and validates an issue type from content.
 // Returns the validated type or error if invalid.
+// Supports type aliases like "enhancement" -> "feature".
 func ParseIssueType(content string) (types.IssueType, error) {
-	issueType := types.IssueType(strings.TrimSpace(content))
+	// Normalize to support aliases like "enhancement" -> "feature"
+	issueType := types.IssueType(strings.TrimSpace(content)).Normalize()
 
 	// Use the canonical IsValid() from types package
 	if !issueType.IsValid() {