test(canvas/ui): add StatusBadge coverage (11 cases)

Covers StatusBadge — secret key connection status indicator:
- ✓ / ✗ / ○ icon per status
- aria-label per status
- className per status (--valid, --invalid, --unverified)
- role="status" set correctly
- Exactly one status element rendered

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canvas/src/components/ui/__tests__/StatusBadge.test.tsx

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+// @vitest-environment jsdom
+/**
+ * StatusBadge — secret key connection status indicator.
+ *
+ * Per spec §4: always icon + color (never colour-only) for colour-blind users.
+ * Covers: verified / invalid / unverified render branches, icon, aria-label, className.
+ */
+import { afterEach, describe, expect, it } from "vitest";
+import { render } from "@testing-library/react";
+import React from "react";
+
+import { StatusBadge } from "../StatusBadge";
+
+afterEach(() => {
+  // Prevent DOM accumulation across tests (maxWorkers=1 means all test
+  // files share the same jsdom worker).
+  const { cleanup } = require("@testing-library/react");
+  cleanup();
+});
+
+function getBadge(status: "verified" | "invalid" | "unverified") {
+  const { container } = render(<StatusBadge status={status} />);
+  return container.querySelector("[role=status]") as HTMLElement;
+}
+
+describe("StatusBadge — icon", () => {
+  it("renders ✓ for verified", () => {
+    expect(getBadge("verified").textContent).toBe("✓");
+  });
+
+  it("renders ✗ for invalid", () => {
+    expect(getBadge("invalid").textContent).toBe("✗");
+  });
+
+  it("renders ○ for unverified", () => {
+    expect(getBadge("unverified").textContent).toBe("○");
+  });
+});
+
+describe("StatusBadge — aria-label", () => {
+  it("sets 'Connection status: verified' for verified", () => {
+    expect(getBadge("verified").getAttribute("aria-label")).toBe(
+      "Connection status: verified",
+    );
+  });
+
+  it("sets 'Connection status: invalid' for invalid", () => {
+    expect(getBadge("invalid").getAttribute("aria-label")).toBe(
+      "Connection status: invalid",
+    );
+  });
+
+  it("sets 'Connection status: unverified' for unverified", () => {
+    expect(getBadge("unverified").getAttribute("aria-label")).toBe(
+      "Connection status: unverified",
+    );
+  });
+});
+
+describe("StatusBadge — className", () => {
+  it("applies status-badge--valid for verified", () => {
+    expect(getBadge("verified").className).toContain("status-badge--valid");
+  });
+
+  it("applies status-badge--invalid for invalid", () => {
+    expect(getBadge("invalid").className).toContain("status-badge--invalid");
+  });
+
+  it("applies status-badge--unverified for unverified", () => {
+    expect(getBadge("unverified").className).toContain(
+      "status-badge--unverified",
+    );
+  });
+});
+
+describe("StatusBadge — role", () => {
+  it("sets role=status", () => {
+    const el = getBadge("verified");
+    expect(el.getAttribute("role")).toBe("status");
+  });
+});
+
+describe("StatusBadge — structural", () => {
+  it("renders exactly one status element", () => {
+    const { container } = render(<StatusBadge status="verified" />);
+    expect(container.querySelectorAll("[role=status]").length).toBe(1);
+  });
+});