feat: add queued status + FIFO queue ordering

- Add Queued variant to VideoStatus enum
- Trigger sets videos.status='queued' instead of staying 'pending'
- Worker sets videos.status='processing' on pickup
- list_monitor_jobs_by_status ORDER BY created_at ASC (FIFO)
- queue_position counts both 'pending' and 'queued' jobs

src/api/processing.rs

@@ -302,7 +302,7 @@ async fn trigger_processing(
         "progress": progress
     });
     sqlx::query(&format!(
-        "UPDATE {videos_table} SET processing_status = $1, updated_at = CURRENT_TIMESTAMP WHERE file_uuid = $2"
+        "UPDATE {videos_table} SET status = 'queued', processing_status = $1, updated_at = CURRENT_TIMESTAMP WHERE file_uuid = $2"
     ))
     .bind(&status)
     .bind(&file_uuid)
@@ -558,10 +558,10 @@ async fn get_job(Path(uuid): Path<String>) -> Result<Json<JobDetailResponse>, St
         updated_at,
     ) = job.ok_or(StatusCode::NOT_FOUND)?;
     
-    // Calculate queue position if status is 'pending'
-    let queue_position = if status == "pending" {
+    // Calculate queue position (pending or queued jobs ahead of this one)
+    let queue_position = if status == "pending" || status == "queued" {
         sqlx::query_scalar::<_, i64>(&format!(
-            "SELECT COUNT(*) + 1 FROM {} WHERE status = 'pending' AND created_at < (SELECT created_at FROM {} WHERE uuid = $1)",
+            "SELECT COUNT(*) + 1 FROM {} WHERE status IN ('pending', 'queued') AND created_at < (SELECT created_at FROM {} WHERE uuid = $1)",
             jobs_table, jobs_table
         ))
         .bind(&uuid)