fix: persist token counts and fix agentic insight_id mapping

- Add prompt_eval_count and eval_count columns to photo_insights so
  token usage from llama-swap/Ollama is stored and returned by the API
- Fix agentic generator return: was (prompt_eval_count, eval_count),
  handler destructured first element as insight_id — now returns
  (insight_id, prompt_eval_count, eval_count)
- Wire prompt_eval_count/eval_count from DB into PhotoInsightResponse
  instead of hardcoded None

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/database/schema.rs

@@ -223,6 +223,8 @@ diesel::table! {
         min_p -> Nullable<Float>,
         system_prompt -> Nullable<Text>,
         persona_id -> Nullable<Text>,
+        prompt_eval_count -> Nullable<Integer>,
+        eval_count -> Nullable<Integer>,
     }
 }