config: tune sack conf to 0.30 and update changelog

CHANGELOG.md

@@ -8,6 +8,13 @@ version tags are cut in this repo — POC stage, `main` is the release line).
 
 Nothing pending.
 
+## 2026-09-18 — Config tuning: Sack confidence and batch timeout
+
+### Changed
+- `config.yaml`: Decreased `models.detection_params.sack.conf` from `0.35` to `0.30` for improved sack sensitivity.
+- `config.yaml`: Decreased `batch.timeout_seconds` from `30.0` to `20.0` for faster batch cycle completion.
+- `config.yaml`: Clarified deprecation note on `batch.merge_threshold_seconds`.
+
 ## 2026-09-17 — Unified `config.yaml` with extensible model presets
 
 ### Added

config.yaml

@@ -83,7 +83,7 @@ models:
       iou: 0.7
       min_bbox_area: 5000
     sack:
-      conf: 0.35
+      conf: 0.3 # default 0.35
       iou: 0.7
       min_bbox_area: 1500
     box: