test(coverage): bootstrap vitest unit infra and add tests at 90%+ per file (#1245) (#1269)

* test(coverage): bootstrap vitest unit infra and add tests at 90%+ per file (#1245)

Establishes the unit-test runtime AGENTS.md mandates: a vitest "unit"
project alongside the existing storybook project, RTL + jest-dom +
happy-dom, a Mantine-aware render helper, and a 90%-line per-file
coverage gate enforced by CI. Adds 66 test files covering all 62
components under elements/groups/screens/views, plus core/mcp and
clients/web/src/utils. Total: 577 tests, 98.7% line coverage globally.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* test(coverage): address PR #1269 review feedback

- AGENTS.md: correct coverage gate description (lines ≥ 90, statements ≥ 85,
  functions ≥ 80, branches ≥ 50) with rationale for the relaxed branch
  threshold
- InspectorView.test.tsx: document what the Math.random() mock values
  (0.1 / 0.99) control vs. STUB_SUCCESS_RATE in InspectorView.tsx
- vite.config.ts / tsconfig.test.json: drop unused `globals: true` and the
  `vitest/globals` type now that every test file imports describe/it/expect/vi
  explicitly; manual `afterEach(cleanup)` in setup.ts remains required because
  testing-library auto-cleanup relies on globalThis.afterEach

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/web/src/components/elements/SubscribeButton/SubscribeButton.test.tsx

@@ -0,0 +1,32 @@
+import { describe, it, expect, vi } from "vitest";
+import { renderWithMantine, screen } from "../../../test/renderWithMantine";
+import userEvent from "@testing-library/user-event";
+import { SubscribeButton } from "./SubscribeButton";
+
+describe("SubscribeButton", () => {
+  it("renders 'Subscribe' when not subscribed", () => {
+    renderWithMantine(
+      <SubscribeButton subscribed={false} onToggle={() => {}} />,
+    );
+    expect(
+      screen.getByRole("button", { name: "Subscribe" }),
+    ).toBeInTheDocument();
+  });
+
+  it("renders 'Unsubscribe' when subscribed", () => {
+    renderWithMantine(<SubscribeButton subscribed onToggle={() => {}} />);
+    expect(
+      screen.getByRole("button", { name: "Unsubscribe" }),
+    ).toBeInTheDocument();
+  });
+
+  it("invokes onToggle on click", async () => {
+    const user = userEvent.setup();
+    const onToggle = vi.fn();
+    renderWithMantine(
+      <SubscribeButton subscribed={false} onToggle={onToggle} />,
+    );
+    await user.click(screen.getByRole("button", { name: "Subscribe" }));
+    expect(onToggle).toHaveBeenCalledTimes(1);
+  });
+});