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/pipeline.py

@@ -49,6 +49,8 @@ class FallPipeline:
         policy: FallEvidencePolicy,
         state_machine: FallStateMachine,
         keypoint_confidence_threshold: float,
+        require_lower_body: bool = True,
+        horizontal_angle_threshold_degrees: float = 35.0,
     ) -> None:
         if not 0.0 <= keypoint_confidence_threshold <= 1.0:
             raise ValueError("keypoint_confidence_threshold must be between 0 and 1")
@@ -57,6 +59,8 @@ class FallPipeline:
         self._policy = policy
         self._state_machine = state_machine
         self._keypoint_confidence_threshold = float(keypoint_confidence_threshold)
+        self._require_lower_body = bool(require_lower_body)
+        self._horizontal_angle_threshold_degrees = float(horizontal_angle_threshold_degrees)
         self._previous_evidence: Dict[str, PoseEvidence] = {}
         self._active_track_ids = set()
 
@@ -74,7 +78,10 @@ class FallPipeline:
         return cls(
             pose_adapter=pose_adapter,
             tracker=PersonTracker(),
-            policy=FallEvidencePolicy(config.event.suspect_window_seconds),
+            policy=FallEvidencePolicy(
+                config.event.suspect_window_seconds,
+                require_rapid_drop=config.event.require_rapid_drop,
+            ),
             state_machine=FallStateMachine(
                 confirm_window_seconds=config.event.confirm_window_seconds,
                 recovery_window_seconds=config.event.recovery_window_seconds,
@@ -83,6 +90,8 @@ class FallPipeline:
                 session_id=session_id or new_session_id(),
             ),
             keypoint_confidence_threshold=config.event.keypoint_confidence_threshold,
+            require_lower_body=config.event.require_lower_body,
+            horizontal_angle_threshold_degrees=config.event.horizontal_angle_threshold_degrees,
         )
 
     def process(self, packet: FramePacket) -> FrameAnalysis:
@@ -102,12 +111,15 @@ class FallPipeline:
         people = []
         for tracked in tracked_poses:
             quality = assess_pose_quality(
-                tracked.pose, threshold=self._keypoint_confidence_threshold
+                tracked.pose,
+                threshold=self._keypoint_confidence_threshold,
+                require_lower_body=self._require_lower_body,
             )
             pose_evidence = extract_evidence(
                 tracked.pose,
                 quality=quality,
                 previous=self._previous_evidence.get(tracked.track_id),
+                horizontal_angle_threshold_degrees=self._horizontal_angle_threshold_degrees,
             )
             state_before = self._state_machine.state_of(tracked.track_id)
             evidence = self._policy.evaluate(