ML-170: add enrichment fields to collection API

Add MusicLibrary.Collection.Enrichment module with batch scrobble, artist
country, and selected release enrichment from existing tables.

Wire enrichment into all four collection API endpoints (index, latest,
random, on_this_day). New JSON fields: scrobble_count, last_listened_at,
artist_country, selected_release.

Uses 3 fixed-count batch queries regardless of page size — no N+1 risk.
No schema changes or migrations required.

lib/music_library_web/controllers/collection_controller.ex

@@ -3,17 +3,26 @@ defmodule MusicLibraryWeb.CollectionController do
 
   alias MusicBrainz
   alias MusicLibrary.Collection
+  alias MusicLibrary.Collection.Enrichment
   alias MusicLibrary.Records
   alias MusicLibrary.ScrobbleActivity
 
   def latest(conn, _params) do
-    latest_record = Collection.get_latest_record!()
+    latest_record =
+      Collection.get_latest_record!()
+      |> List.wrap()
+      |> Enrichment.enrich()
+      |> hd()
 
     render(conn, :show, record: latest_record)
   end
 
   def random(conn, _params) do
-    random_record = Collection.get_random_record!()
+    random_record =
+      Collection.get_random_record!()
+      |> List.wrap()
+      |> Enrichment.enrich()
+      |> hd()
 
     render(conn, :show, record: random_record)
   end
@@ -25,7 +34,10 @@ defmodule MusicLibraryWeb.CollectionController do
         date_string -> Date.from_iso8601!(date_string)
       end
 
-    records_on_this_day = Collection.get_records_on_this_day(current_date)
+    records_on_this_day =
+      current_date
+      |> Collection.get_records_on_this_day()
+      |> Enrichment.enrich()
 
     render(conn, :on_this_day, records: records_on_this_day)
   end
@@ -37,7 +49,10 @@ defmodule MusicLibraryWeb.CollectionController do
 
     total = Collection.search_records_count(query)
 
-    records = Collection.search_records(query, limit: limit, offset: offset)
+    records =
+      query
+      |> Collection.search_records(limit: limit, offset: offset)
+      |> Enrichment.enrich()
 
     render(conn, :index, total: total, limit: limit, offset: offset, records: records)
   end