feat: start on AI integration

priv/repo/migrations/20260424110431_add_ai_chat_usage_fields.exs

@@ -0,0 +1,12 @@
+defmodule BDS.Repo.Migrations.AddAiChatUsageFields do
+  use Ecto.Migration
+
+  def change do
+    alter table(:chat_messages) do
+      add :token_usage_input, :integer
+      add :token_usage_output, :integer
+      add :cache_read_tokens, :integer
+      add :cache_write_tokens, :integer
+    end
+  end
+end