chore: reconcile the catalogue and metric-unit guards

The widget catalogue grew to 42 ids, so the snapshot round-trip count
follows. The mood card's unit key carries "/5" rather than an empty
string — the locale-integrity guard forbids empty values, and the scale
is the honest thing to print next to a 1-to-5 score. It joins the
identical-across-locales allowlist alongside the other unit notations.

src/lib/dashboard-layout.ts

@@ -605,8 +605,6 @@ export const LAYOUT_FIELD_MERGE_DISPOSITION = {
   heroRingOrder: "preserve",
 } as const satisfies Record<keyof DashboardLayout, "replace" | "preserve">;
 
-export type LayoutFieldMergeDisposition = typeof LAYOUT_FIELD_MERGE_DISPOSITION;
-
 /**
  * The top-level layout fields the widgets PUT carries forward from the stored
  * layout when the request omits them. Derived from