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/fall_policy.py

@@ -9,8 +9,11 @@ from v1.fall_state import Evidence, FallState
 class FallEvidencePolicy:
     """Require a recent rapid drop before a horizontal pose becomes a candidate."""
 
-    def __init__(self, suspect_window_seconds: float) -> None:
+    def __init__(
+        self, suspect_window_seconds: float, require_rapid_drop: bool = True
+    ) -> None:
         self._suspect_window_seconds = float(suspect_window_seconds)
+        self._require_rapid_drop = bool(require_rapid_drop)
         self._rapid_drop_at: Dict[str, float] = {}
 
     def evaluate(
@@ -30,8 +33,13 @@ class FallEvidencePolicy:
         candidate = False
         if state is FallState.SUSPECT:
             candidate = pose_evidence.horizontal_pose
-        elif pose_evidence.horizontal_pose and track_id in self._rapid_drop_at:
-            candidate = timestamp - self._rapid_drop_at[track_id] <= self._suspect_window_seconds
+        elif pose_evidence.horizontal_pose:
+            if not self._require_rapid_drop:
+                candidate = True
+            elif track_id in self._rapid_drop_at:
+                candidate = (
+                    timestamp - self._rapid_drop_at[track_id] <= self._suspect_window_seconds
+                )
 
         recovery = (
             state in (FallState.CONFIRMED, FallState.RECOVERING)