Add 'molecule' as valid issue type

Molecules are composable workflow templates used by Gas Town (gt) for
defining multi-step processes like bootstrap, engineer-in-box, etc.

Changes:
- Add TypeMolecule constant to internal/types/types.go
- Add molecule to IsValid() switch case
- Add molecule and merge-request to validation/bead.go validTypes map
- Update help text in create.go, show.go, list.go
- Add test cases for molecule and merge-request types

Closes gt-qn4l

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

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

cmd/bd/create.go

@@ -392,7 +392,7 @@ func init() {
 	createCmd.Flags().String("title", "", "Issue title (alternative to positional argument)")
 	createCmd.Flags().Bool("silent", false, "Output only the issue ID (for scripting)")
 	registerPriorityFlag(createCmd, "2")
-	createCmd.Flags().StringP("type", "t", "task", "Issue type (bug|feature|task|epic|chore|merge-request)")
+	createCmd.Flags().StringP("type", "t", "task", "Issue type (bug|feature|task|epic|chore|merge-request|molecule)")
 	registerCommonIssueFlags(createCmd)
 	createCmd.Flags().StringSliceP("labels", "l", []string{}, "Labels (comma-separated)")
 	createCmd.Flags().StringSlice("label", []string{}, "Alias for --labels")

cmd/bd/list.go

@@ -547,7 +547,7 @@ func init() {
 	listCmd.Flags().StringP("status", "s", "", "Filter by status (open, in_progress, blocked, closed)")
 	registerPriorityFlag(listCmd, "")
 	listCmd.Flags().StringP("assignee", "a", "", "Filter by assignee")
-	listCmd.Flags().StringP("type", "t", "", "Filter by type (bug, feature, task, epic, chore, merge-request)")
+	listCmd.Flags().StringP("type", "t", "", "Filter by type (bug, feature, task, epic, chore, merge-request, molecule)")
 	listCmd.Flags().StringSliceP("label", "l", []string{}, "Filter by labels (AND: must have ALL). Can combine with --label-any")
 	listCmd.Flags().StringSlice("label-any", []string{}, "Filter by labels (OR: must have AT LEAST ONE). Can combine with --label")
 	listCmd.Flags().String("title", "", "Filter by title text (case-insensitive substring match)")

cmd/bd/show.go

@@ -1338,7 +1338,7 @@ func init() {
 	updateCmd.Flags().StringP("status", "s", "", "New status")
 	registerPriorityFlag(updateCmd, "")
 	updateCmd.Flags().String("title", "", "New title")
-	updateCmd.Flags().StringP("type", "t", "", "New type (bug|feature|task|epic|chore|merge-request)")
+	updateCmd.Flags().StringP("type", "t", "", "New type (bug|feature|task|epic|chore|merge-request|molecule)")
 	registerCommonIssueFlags(updateCmd)
 	updateCmd.Flags().String("notes", "", "Additional notes")
 	updateCmd.Flags().String("acceptance-criteria", "", "DEPRECATED: use --acceptance")