feat: surface session goal evaluation model and add diagnostics

Shows the evaluation provider/model used for the latest successful goal audit in the UI.
Persists evaluation model metadata on session goals and covers it in tests.
Adds diagnostic logging for small-model calls and session-goal audit parsing.

packages/ui/src/lib/i18n/messages/ja.ts

@@ -1412,6 +1412,7 @@ export const dict: Record<I18nKey, string> = {
   'chat.goal.dialog.objectiveLabel': '目標',
   'chat.goal.dialog.objectivePlaceholder': 'エージェントが到達して検証すべき最終状態を記述してください…',
   'chat.goal.dialog.budgetLabel': 'トークン予算',
+  'chat.goal.dialog.evaluationModelLabel': '評価モデル',
   'chat.goal.status.active': '進行中',
   'chat.goal.status.evaluating': '評価中…',
   'chat.goal.status.paused': '一時停止',