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/ai/insight_chat.rs

@@ -524,6 +524,8 @@ impl InsightChatService {
                 min_p: req.min_p,
                 system_prompt: req.system_prompt.clone(),
                 persona_id: req.persona_id.clone(),
+                prompt_eval_count: None,
+                eval_count: None,
             };
             let cx = opentelemetry::Context::new();
             let mut dao = self.insight_dao.lock().expect("Unable to lock InsightDao");
@@ -878,6 +880,8 @@ impl InsightChatService {
                 min_p: req.min_p,
                 system_prompt: req.system_prompt.clone(),
                 persona_id: req.persona_id.clone(),
+                prompt_eval_count: None,
+                eval_count: None,
             };
             let cx = opentelemetry::Context::new();
             let mut dao = self.insight_dao.lock().expect("Unable to lock InsightDao");
@@ -1073,6 +1077,8 @@ impl InsightChatService {
             min_p: req.min_p,
             system_prompt: req.system_prompt.clone(),
             persona_id: req.persona_id.clone(),
+            prompt_eval_count: None,
+            eval_count: None,
         };
         let stored = {
             let cx = opentelemetry::Context::new();