feat(notifications): auto-dismiss loading OSD on overlay visibility chan

- add dismissOverlayLoadingOsd dep and call it on hide/show paths (macOS only)
- simplify notification card styles: remove accent bar, flatten gradient bg, tweak spacing
- fix test CSS path to use __dirname instead of process.cwd()

src/main.ts

@@ -2651,6 +2651,9 @@ const overlayVisibilityRuntime = createOverlayVisibilityRuntimeService(
     showOverlayLoadingOsd: (message: string) => {
       showOverlayLoadingStatusNotification(message);
     },
+    dismissOverlayLoadingOsd: () => {
+      dismissOverlayNotification('overlay-loading-status');
+    },
     hideNonNativeOverlayWhenTargetUnfocused: () =>
       shouldRunLinuxOverlayZOrderKeepAlive() &&
       linuxVisibleOverlayWindowMode === 'fullscreen-override',