test(contracts): whitelist the unified row's two new keys on search rows

The H4 row-completion commit made abridged/audio_metadata emit on the
search wire (the endpoint serializes the row directly) — exactly what
the pin exists to surface. Whitelisted per the additive rule with the
changelog entry.

docs/contract_pins.md

@@ -87,3 +87,8 @@ cover_image_path, has_conflict, format_group, badge`.
   `last_modified_at` are now maintained. Note PUT unchanged on the wire
   (content+position) but routed through the service the same way.
   Response shapes unchanged (same row models — pins green).
+- **H4 (unified row completion)** — `/api/media-items/search` rows[]
+  whitelisted ADDITIVE keys `abridged, audio_metadata`: the unified
+  search row gained the two columns it lagged (EXPLAIN plan-identical —
+  both ride the already-scanned media_items side), and the endpoint
+  serializes the row directly, so they emit. No key removed or renamed.