feat(ui/alerts): TanStack Query hooks for /alerts endpoints

Adds env-scoped hooks for the alerts inbox:
- useAlerts (30s poll, background-paused, filter-aware)
- useAlert, useUnreadCount (30s poll)
- useAckAlert, useMarkAlertRead, useBulkReadAlerts (mutations that
  invalidate the alerts query key tree + unread-count)

Test file uses .tsx because the QueryClientProvider wrapper relies on
JSX; vitest picks up both .ts and .tsx via the configured include glob.
Client mock targets the actual export name (`api` in ../client) rather
than the `apiClient` alias that alertMeta re-exports.

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

ui/src/api/queries/alerts.test.tsx

@@ -0,0 +1,73 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { renderHook, waitFor } from '@testing-library/react';
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
+import type { ReactNode } from 'react';
+import { useEnvironmentStore } from '../environment-store';
+
+vi.mock('../client', () => ({
+  api: { GET: vi.fn(), POST: vi.fn() },
+}));
+
+import { api as apiClient } from '../client';
+import { useAlerts, useUnreadCount } from './alerts';
+
+function wrapper({ children }: { children: ReactNode }) {
+  const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+  return <QueryClientProvider client={qc}>{children}</QueryClientProvider>;
+}
+
+describe('useAlerts', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    useEnvironmentStore.setState({ environment: 'dev' });
+  });
+
+  it('fetches alerts for selected env and passes filter query params', async () => {
+    (apiClient.GET as any).mockResolvedValue({ data: [], error: null });
+    const { result } = renderHook(
+      () => useAlerts({ state: 'FIRING', severity: ['CRITICAL', 'WARNING'] }),
+      { wrapper },
+    );
+    await waitFor(() => expect(result.current.isSuccess).toBe(true));
+    expect(apiClient.GET).toHaveBeenCalledWith(
+      '/environments/{envSlug}/alerts',
+      expect.objectContaining({
+        params: expect.objectContaining({
+          path: { envSlug: 'dev' },
+          query: expect.objectContaining({
+            state: ['FIRING'],
+            severity: ['CRITICAL', 'WARNING'],
+            limit: 100,
+          }),
+        }),
+      }),
+    );
+  });
+
+  it('does not fetch when no env is selected', () => {
+    useEnvironmentStore.setState({ environment: undefined });
+    const { result } = renderHook(() => useAlerts(), { wrapper });
+    expect(result.current.fetchStatus).toBe('idle');
+    expect(apiClient.GET).not.toHaveBeenCalled();
+  });
+});
+
+describe('useUnreadCount', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    useEnvironmentStore.setState({ environment: 'dev' });
+  });
+
+  it('returns the server payload unmodified', async () => {
+    (apiClient.GET as any).mockResolvedValue({
+      data: { total: 3, bySeverity: { CRITICAL: 1, WARNING: 2, INFO: 0 } },
+      error: null,
+    });
+    const { result } = renderHook(() => useUnreadCount(), { wrapper });
+    await waitFor(() => expect(result.current.isSuccess).toBe(true));
+    expect(result.current.data).toEqual({
+      total: 3,
+      bySeverity: { CRITICAL: 1, WARNING: 2, INFO: 0 },
+    });
+  });
+});