Expose ComfyUI run time on Enhance jobs as run_ms

Parse execution_start vs the end event from /history, store it when the
poller moves a job to ready/failed (never overwritten with null), and
return it as "run_ms" on every job endpoint.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/enhance/service.rs

@@ -361,6 +361,7 @@ impl EnhanceService {
             discarded: 0,
             created_at: now,
             updated_at: now,
+            run_ms: None,
         };
         self.dao
             .lock()
@@ -520,6 +521,7 @@ impl EnhanceService {
                     .error
                     .unwrap_or_else(|| "ComfyUI reported an error".to_string()),
             );
+            u.run_ms = entry.run_ms;
             self.update_job(&job.id, &u);
             return;
         }
@@ -531,6 +533,7 @@ impl EnhanceService {
         }
         let mut u = JobUpdate::status(STATUS_READY);
         u.pending = serde_json::to_string(&entry.staged).ok();
+        u.run_ms = entry.run_ms;
         self.update_job(&job.id, &u);
         info!(
             "enhance: job {} ready ({} result(s))",