feat(v1): edit detection sensitivity from the settings tab

Adds write_local_event_tuning and a sensitivity group (confirm window,
horizontal angle, require-rapid-drop, require-lower-body) that persists to
the untracked local config and applies next start. 79 tests pass.

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

v1/config.py

@@ -196,6 +196,31 @@ def write_local_camera_source(
     return path
 
 
+def write_local_event_tuning(
+    config_path: Path,
+    require_rapid_drop: bool,
+    require_lower_body: bool,
+    horizontal_angle_threshold_degrees: float,
+    confirm_window_seconds: float,
+) -> Path:
+    """Persist detection-sensitivity tuning into the local config's event block.
+
+    Only the tuning keys are updated; other event fields are preserved. Applies
+    at the next start (the running config is a start-time snapshot).
+    """
+
+    path = Path(config_path)
+    data = json.loads(path.read_text(encoding="utf-8"))
+    event = dict(data.get("event", {}))
+    event["require_rapid_drop"] = bool(require_rapid_drop)
+    event["require_lower_body"] = bool(require_lower_body)
+    event["horizontal_angle_threshold_degrees"] = float(horizontal_angle_threshold_degrees)
+    event["confirm_window_seconds"] = float(confirm_window_seconds)
+    data["event"] = event
+    path.write_text(json.dumps(data, ensure_ascii=False, indent=2) + "\n", encoding="utf-8")
+    return path
+
+
 def load_config(path: Path) -> AppConfig:
     """Load one public/local configuration pair without persisting credentials.