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/handlers.rs

@@ -85,6 +85,8 @@ pub struct JobView {
     reference_path: Option<String>,
     created_at: i64,
     updated_at: i64,
+    /// Milliseconds ComfyUI ran the job; null until it has finished.
+    run_ms: Option<i64>,
     pending: Vec<PendingView>,
     saved: Vec<SavedView>,
 }
@@ -118,6 +120,7 @@ pub fn job_view(job: &EnhanceJobRow) -> JobView {
         reference_path: job.reference_path.clone(),
         created_at: job.created_at,
         updated_at: job.updated_at,
+        run_ms: job.run_ms,
         pending,
         saved: saved
             .into_iter()