fix: export JournalImageVariant from one auto-imported file

- types.ts re-exported the interface srcset.ts declares, so every build of
  an app with the layer warned Duplicated imports "JournalImageVariant"
- a test checks that every name of app/utils and app/composables has one
  home

app/utils/types.ts

@@ -4,8 +4,6 @@
 
 import type { JournalImageVariant } from './srcset.ts'
 
-export type { JournalImageVariant }
-
 /** The author object embedded in a post row. `null` when the post has none. */
 export interface JournalAuthorRef {
   id: number