fix(convoy): ensure custom types registered before creating convoy

Call beads.EnsureCustomTypes before attempting to create a convoy.
This fixes invalid issue type: convoy errors that occur when town
beads do not have custom types configured (e.g., incomplete install
or manually initialized beads).

The EnsureCustomTypes function uses caching (in-memory + sentinel file)
so this adds negligible overhead to convoy create.

Fixes: gt-1b8eg9

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

internal/cmd/convoy.go

@@ -309,6 +309,12 @@ func runConvoyCreate(cmd *cobra.Command, args []string) error {
 		return err
 	}
 
+	// Ensure custom types (including 'convoy') are registered in town beads.
+	// This handles cases where install didn't complete or beads was initialized manually.
+	if err := beads.EnsureCustomTypes(townBeads); err != nil {
+		return fmt.Errorf("ensuring custom types: %w", err)
+	}
+
 	// Create convoy issue in town beads
 	description := fmt.Sprintf("Convoy tracking %d issues", len(trackedIssues))