fix(dashboard): F-U-009 add download link + copy-id button per file row

Listing showed name/content-type/size/created/id; only mutation was
Delete. No download link, no copy-id button (the UUID was rendered
unclickable), no preview, no metadata refresh. Operators had to use
the admin API directly.

- Add api.files.downloadUrl(slug, collection, id) helper that builds
  the admin GET URL. The anchor uses HTML `download` so the browser
  saves with the original filename.
- Add a ⧉ copy-id button next to the UUID column using
  navigator.clipboard.writeText. Silently no-ops where the browser
  doesn't expose clipboard (plain-http LAN).
- Preview / metadata-refresh are deferred to a UI overhaul.

AUDIT.md anchor: F-U-009 (partial — download + copy; preview deferred).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

dashboard/src/lib/api.ts

@@ -907,7 +907,11 @@ export const api = {
 			adminRequest<null>(
 				`/api/v1/admin/apps/${encodeURIComponent(idOrSlug)}/files/${encodeURIComponent(collection)}/${fileId}`,
 				{ method: 'DELETE' }
-			)
+			),
+		/// F-U-009: build the admin download URL. GET returns the file
+		/// bytes inline; the browser handles content-disposition.
+		downloadUrl: (idOrSlug: string, collection: string, fileId: string): string =>
+			`/api/v1/admin/apps/${encodeURIComponent(idOrSlug)}/files/${encodeURIComponent(collection)}/${fileId}`
 	},
 
 	secrets: {