feat: Phase 2+3 frontend coverage — responsive + accessibility tests + CI threshold

- Viewer accessibility: 5 tests (aria-labels, aria-expanded, label association, alert role)
- Viewer responsive: 3 tests (chat-collapsed, CSS grid, now-playing aria-live)
- Admin accessibility: 3 tests (nav aria-label, aria-current, focusability)
- Admin responsive: 2 tests (tab visibility, essential tabs)
- Coverage: vitest v8 provider, 40% stmt/lines, 30% branches/funcs
- CI: test:coverage step between lint and build
- Total: 44 frontend tests (31 + 13 new)
- Updated TODO.md (Phase 2+3 done), DONE.md, MEMORY.md

frontend/src/main.test.ts

@@ -371,3 +371,68 @@ describe("player error recovery", () => {
     }
   });
 });
+
+describe("accessibility", () => {
+  it("player video has controls and aria attributes", () => {
+    const video = document.getElementById("player") as HTMLVideoElement;
+    expect(video.controls).toBe(true);
+    expect(video.hasAttribute("autoplay")).toBe(true);
+    expect(video.hasAttribute("playsinline")).toBe(true);
+  });
+
+  it("chat panel has aria-labels for live region", () => {
+    const messages = document.getElementById("messages");
+    expect(messages?.getAttribute("aria-live")).toBe("polite");
+
+    const chatPanel = document.getElementById("chat-panel");
+    expect(chatPanel?.getAttribute("aria-label")).toBe("Chat panel");
+  });
+
+  it("chat toggle exposes aria-expanded state", () => {
+    const toggle = document.getElementById("chat-toggle")!;
+    expect(toggle.getAttribute("aria-expanded")).toBe("true");
+
+    window.toggleChatPanel();
+    expect(toggle.getAttribute("aria-expanded")).toBe("false");
+  });
+
+  it("message input has associated label", () => {
+    const input = document.getElementById("message-input") as HTMLInputElement;
+    expect(input.getAttribute("type")).toBe("text");
+    expect(input.placeholder).toBe("Type a message...");
+    const label = document.querySelector("label[for='message-input']");
+    expect(label).toBeTruthy();
+    expect(label?.textContent).toBe("Message input");
+  });
+
+  it("reconnecting overlay is an aria-live assertive region", () => {
+    const overlay = document.getElementById("reconnecting-overlay");
+    expect(overlay?.getAttribute("role")).toBe("alert");
+    expect(overlay?.getAttribute("aria-live")).toBe("assertive");
+  });
+});
+
+describe("responsive layout", () => {
+  it("chat-collapsed class hides sidebar at narrow viewport", () => {
+    const shell = document.querySelector(".viewer-shell")!;
+    expect(shell.classList.contains("chat-collapsed")).toBe(false);
+
+    window.toggleChatPanel();
+    expect(shell.classList.contains("chat-collapsed")).toBe(true);
+
+    window.toggleChatPanel();
+    expect(shell.classList.contains("chat-collapsed")).toBe(false);
+  });
+
+  it("viewer-shell uses CSS grid for content layout", () => {
+    const content = document.querySelector(".viewer-content");
+    expect(content).toBeTruthy();
+    const style = window.getComputedStyle(content!);
+    expect(style.display).toBe("grid");
+  });
+
+  it("now-playing overlay is accessible at small sizes", () => {
+    const np = document.getElementById("now-playing");
+    expect(np?.getAttribute("aria-live")).toBe("polite");
+  });
+});