Refactor into modular app structure

Split monolithic files into focused modules:
- app/core: settings, logging, lifecycle
- app/signaling: websocket server, ICE parser, message models
- app/webrtc: peer session, video receiver, frame source
- app/vision: pose landmarker wrapper, model config, pose types
- app/exercises/dead_bug: detector, metrics, rules, state machine, types
- app/rendering: skeleton renderer, status overlay, window display
- app/audio: rep announcer
- app/diagnostics: perf timer, crash handler
- configs: environment-based settings
- tests: unit tests for rules, state machine, ICE parser
- run.py: entry point

tests/test_dead_bug_rules.py

@@ -0,0 +1,65 @@
+from __future__ import annotations
+
+from app.exercises.dead_bug.metrics import calculate_metrics
+from app.exercises.dead_bug.rules import detect_diagonal_extension, has_required_visibility, is_ready_position
+from app.exercises.dead_bug.state_machine import DeadBugStateMachine
+from app.exercises.dead_bug.types import DeadBugMetrics, DeadBugPhase, Point
+
+
+class TestDeadBugRules:
+    def _make_landmark(self, x=0.5, y=0.5, z=0.0, visibility=1.0):
+        return Point(x, y, z, visibility)
+
+    def _make_visible_landmarks(self):
+        return [self._make_landmark() for _ in range(33)]
+
+    def test_has_required_visibility_all_visible(self):
+        lm = self._make_visible_landmarks()
+        indices = (11, 12, 13, 14, 15, 16, 23, 24, 25, 26, 27, 28)
+        assert has_required_visibility(lm, indices, 0.45)
+
+    def test_has_required_visibility_low(self):
+        lm = self._make_visible_landmarks()
+        lm[11] = self._make_landmark(visibility=0.1)
+        indices = (11, 12, 13, 14, 15, 16, 23, 24, 25, 26, 27, 28)
+        assert not has_required_visibility(lm, indices, 0.45)
+
+    def test_detect_diagonal_extension_none(self):
+        metrics = DeadBugMetrics(
+            left_arm_extended=False, right_arm_extended=False,
+            left_leg_extended=False, right_leg_extended=False,
+            left_elbow_angle=90, right_elbow_angle=90,
+            left_knee_angle=90, right_knee_angle=90,
+            feedback=[],
+        )
+        assert detect_diagonal_extension(metrics) is None
+
+    def test_detect_diagonal_extension_left_arm_right_leg(self):
+        metrics = DeadBugMetrics(
+            left_arm_extended=True, right_arm_extended=False,
+            left_leg_extended=False, right_leg_extended=True,
+            left_elbow_angle=160, right_elbow_angle=90,
+            left_knee_angle=90, right_knee_angle=160,
+            feedback=[],
+        )
+        assert detect_diagonal_extension(metrics) == "left_arm_right_leg"
+
+    def test_is_ready_position(self):
+        metrics = DeadBugMetrics(
+            left_arm_extended=False, right_arm_extended=False,
+            left_leg_extended=False, right_leg_extended=False,
+            left_elbow_angle=90, right_elbow_angle=90,
+            left_knee_angle=100, right_knee_angle=100,
+            feedback=[],
+        )
+        assert is_ready_position(metrics)
+
+    def test_is_not_ready_legs_extended(self):
+        metrics = DeadBugMetrics(
+            left_arm_extended=False, right_arm_extended=False,
+            left_leg_extended=True, right_leg_extended=False,
+            left_elbow_angle=90, right_elbow_angle=90,
+            left_knee_angle=100, right_knee_angle=100,
+            feedback=[],
+        )
+        assert not is_ready_position(metrics)