feat: add live camera multi-device viewer mode

tests/e2e/app.spec.ts

@@ -68,6 +68,16 @@ test("live camera starts analysis and produces scores", async ({ page }) => {
   await expect(page.getByTestId("live-camera-score-overall")).toBeVisible();
 });
 
+test("live camera switches into viewer mode when another device already owns analysis", async ({ page }) => {
+  await installAppMocks(page, { authenticated: true, liveViewerMode: true });
+
+  await page.goto("/live-camera");
+  await expect(page.getByText("同步观看模式")).toBeVisible();
+  await expect(page.getByText(/同步观看|重新同步/).first()).toBeVisible();
+  await expect(page.getByText("当前设备已锁定为观看模式")).toBeVisible();
+  await expect(page.getByTestId("live-camera-score-overall")).toBeVisible();
+});
+
 test("live camera archives overlay videos into the library after analysis stops", async ({ page }) => {
   await installAppMocks(page, { authenticated: true, videos: [] });