Add dashboard shell with sidebar nav and version header.

Replace the health-check stub UI with a left menu and content panel so section navigation and frontend/backend versions are visible in the shell.

webui/src/api/client.test.ts

@@ -1,5 +1,5 @@
 import { afterEach, describe, expect, it, vi } from 'vitest'
-import { fetchHealth, getApiBaseUrl } from './client'
+import { fetchHealth, fetchStatus, getApiBaseUrl } from './client'
 
 describe('getApiBaseUrl', () => {
   it('defaults to localhost:8080 when unset', () => {
@@ -36,3 +36,35 @@ describe('fetchHealth', () => {
     )
   })
 })
+
+describe('fetchStatus', () => {
+  afterEach(() => {
+    vi.restoreAllMocks()
+  })
+
+  it('returns parsed status payload', async () => {
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: true,
+      json: async () => ({ service: 'clustercanvas', version: '0.1.0' }),
+    })
+
+    const status = await fetchStatus(fetchMock)
+
+    expect(fetchMock).toHaveBeenCalledWith(
+      'http://localhost:8080/api/v1/status',
+    )
+    expect(status).toEqual({ service: 'clustercanvas', version: '0.1.0' })
+  })
+
+  it('throws when the response is not ok', async () => {
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: false,
+      status: 503,
+      json: async () => ({}),
+    })
+
+    await expect(fetchStatus(fetchMock)).rejects.toThrow(
+      'status check failed: 503',
+    )
+  })
+})