feat(v1): relax fall sensitivity for low overhead cameras

Adds configurable event.require_rapid_drop (default off), require_lower_body
(default off) and horizontal_angle_threshold_degrees (default 45). With the
lenient defaults a sustained horizontal pose alone enters SUSPECT and confirms
after the confirm window, which is now the main false-positive guard; missing
knees/ankles no longer reject the pose. Thresholds flow into config_version.
End-to-end smoke confirms a lying pose; 70 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

v1/config.example.json

@@ -17,7 +17,10 @@
     "suspect_window_seconds": 0.5,
     "confirm_window_seconds": 1.8,
     "recovery_window_seconds": 2.0,
-    "cooldown_seconds": 10.0
+    "cooldown_seconds": 10.0,
+    "require_rapid_drop": false,
+    "require_lower_body": false,
+    "horizontal_angle_threshold_degrees": 45.0
   },
   "artifacts": {
     "event_dir": "../artifacts/events"