Shrink collection summary to fit OpenAI token limit

Deduplicate records by musicbrainz_id (merging formats)
and cap genres to 3 per record, reducing the summary from
~32K to ~24K estimated tokens.

lib/music_library/chats/collection_chat.ex

@@ -8,9 +8,10 @@ defmodule MusicLibrary.Chats.CollectionChat do
   alias MusicLibrary.Chats.Prompt
 
   @impl true
-  @spec stream_response([map()], String.t(), (String.t() -> any())) :: :ok | {:error, term()}
-  def stream_response(messages, collection_summary, callback) do
-    instructions = build_instructions(collection_summary)
+  @spec stream_response([map()], {String.t(), non_neg_integer()}, (String.t() -> any())) ::
+          :ok | {:error, term()}
+  def stream_response(messages, {summary, record_count}, callback) do
+    instructions = build_instructions(summary, record_count)
 
     OpenAI.chat_stream(messages,
       on_chunk: callback,
@@ -19,9 +20,7 @@ defmodule MusicLibrary.Chats.CollectionChat do
     )
   end
 
-  defp build_instructions(collection_summary) do
-    record_count = count_records(collection_summary)
-
+  defp build_instructions(collection_summary, record_count) do
     Prompt.build("""
     Answer questions about the user's music collection. \
     Use the provided collection catalog as your primary reference. \
@@ -31,12 +30,4 @@ defmodule MusicLibrary.Chats.CollectionChat do
     #{collection_summary}\
     """)
   end
-
-  defp count_records(""), do: 0
-
-  defp count_records(summary) do
-    summary
-    |> String.split("\n")
-    |> length()
-  end
 end