refactor: remove Rule 3, Story, and Caption processors

- Remove Rule 3 (Scene Chunking) from worker auto-trigger
- Remove rule3_ingest.rs and related imports
- Remove Story/Caption from playground module parsing
- Clean up scan.rs Rule 3 display
- Fix ASRX field name conversion (start_time -> start)

Reason: Story/5W1H/Scene accuracy too poor - will redesign later

src/api/scan.rs

@@ -462,14 +462,9 @@ async fn get_ingestion_status(
             "auto_vectorize",
             sentence_embedded > 0,
             Some(format!("{sentence_embedded} embedded"))
-        ),
-        step!(
-            "rule3_scene",
-            scene_count > 0,
-            Some(format!("{scene_count} scene chunks"))
-        ),
-        step!(
-            "face_track",
+),
+step!(
+"face_track",
             trace_count > 0,
             Some(format!("{trace_count} traces / {face_total} detections"))
         ),