fix(auto-batch): truck presence needs 50% polygon overlap, config-authoritative timers

Big docked truck bbox rests 1-2px past detection_polygon bottom edge, so
100%-containment made truck_in_area flicker False -> batch 15 split (6+276)
on 2026-09-29 while the truck never left. v4-best.engine detected it at
conf 0.92-0.97 in every replayed frame (no model miss, no retraining).

- truck gate: frac_inside >= 0.5 instead of contains(bbox)
- batch.truck_gone_tolerance_seconds (new, 30) authoritative; drop the
  hardcoded batch_mgr._truck_gone_tolerance = 30.0 override;
  batch.timeout_seconds documented as sack-idle pause only
- [TRUCK] truck_in_area transition debug log

tests/test_config_loader.py

@@ -42,6 +42,9 @@ def test_repo_config_loads_and_validates(repo_config_path):
 def test_do_block_and_batch_default_mode(repo_config_path):
     cfg = load_config(repo_config_path)
     assert cfg.batch.default_mode == "auto"
+    # timeout_seconds = sack-idle (pause); truck_gone_tolerance_seconds = finalize
+    assert cfg.batch.timeout_seconds == 20.0
+    assert cfg.batch.truck_gone_tolerance_seconds == 30.0
     assert cfg.do.enabled is True
     assert cfg.do.require_do is True
     assert cfg.do.require_plate is False
@@ -61,9 +64,11 @@ def test_do_block_missing_uses_defaults(tmp_path):
     raw = yaml.safe_load(p.read_text())
     del raw["do"]
     raw["batch"].pop("default_mode", None)
+    raw["batch"].pop("truck_gone_tolerance_seconds", None)
     p.write_text(yaml.safe_dump(raw))
     cfg = load_config(p)
     assert cfg.batch.default_mode == "auto"
+    assert cfg.batch.truck_gone_tolerance_seconds == 30.0
     assert cfg.do.enabled is True
     assert cfg.do.ocr.engine == "rapid"
     assert cfg.do.retention_days == 7