test(infra): mountWithProviders helper + Vuetify CT sanity test

B2 of TEST-INFRA-001 (RFC-WS-FRONTEND-PRIMEVUE Amendment A-1).

- Add tests/playwright-ct/utils/mountWithProviders.ts: ergonomic
  wrapper around Playwright CT's mount() exposing buildMountArgs()
  and readNotificationState(). Documents the Vue Test Utils ↔
  Playwright CT API divergence (provider plugins must be wired in
  beforeMount, not at call time) and the Vuetify-temp lifecycle
  (replaced by PrimeVue in F3).
- Add tests/playwright-ct/components/SanityButtonHarness.vue: a
  v-btn harness with a click counter; lives in a .vue file so Vite
  bundles its CSS-side-effect imports for the browser context
  (Playwright CT runs the test orchestrator in Node and components
  in a Vite-bundled browser, unlike Vitest's single jsdom graph).
- Add tests/playwright-ct/components/sanity-vuetify.spec.ts: two
  tests proving (a) v-btn renders and propagates clicks, (b) the
  --v-theme-primary CSS variable resolves to a parseable RGB triplet.
- Update playwright/index.ts: import 'vuetify/styles' so the v-btn
  renders with its actual visual appearance (not unstyled). Required
  for B3's visual baselines.

3 component tests pass. 402 Vitest tests still pass unchanged.
Lint + typecheck clean on new files.

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

apps/app/tests/playwright-ct/components/SanityButtonHarness.vue

@@ -0,0 +1,20 @@
+<script setup lang="ts">
+import { ref } from 'vue'
+
+const count = ref(0)
+function onClick() {
+  count.value += 1
+}
+</script>
+
+<template>
+  <div data-test="harness">
+    <VBtn
+      color="primary"
+      data-test="btn"
+      @click="onClick"
+    >
+      Clicks: {{ count }}
+    </VBtn>
+  </div>
+</template>

apps/app/tests/playwright-ct/components/sanity-vuetify.spec.ts

@@ -0,0 +1,50 @@
+import { expect, test } from '@playwright/experimental-ct-vue'
+import SanityButtonHarness from './SanityButtonHarness.vue'
+
+// B2 sanity — proves the full provider stack from playwright/index.ts
+// is wired:
+//   - Vuetify renders v-btn with theme tokens applied
+//   - Click events propagate via Vue's reactivity (counter ref updates)
+//   - Vuetify CSS variables resolve in computed style
+//
+// TEMPORARY VUETIFY: this test is replaced by a PrimeVue equivalent
+// in F3. Do not extend or generalise — F3 rewrites it. See
+// dev-docs/ARCH-TESTING.md §6.
+//
+// Why a .vue harness file: Playwright CT runs the test orchestrator
+// in Node and the component in a Vite-bundled browser context. Vue
+// components that pull in CSS-side-effect imports (Vuetify) cannot be
+// loaded directly into the test's Node module graph; they must live
+// in a .vue / Vite-compilable file. This is a structural divergence
+// from Vitest, which uses jsdom and one module graph for both.
+
+test.describe('B2 sanity: provider stack', () => {
+  test('mounts a Vuetify v-btn and propagates clicks', async ({ mount }) => {
+    const component = await mount(SanityButtonHarness)
+    const btn = component.locator('[data-test="btn"]')
+
+    await expect(btn).toBeVisible()
+    await expect(btn).toContainText('Clicks: 0')
+
+    await btn.click()
+    await expect(btn).toContainText('Clicks: 1')
+
+    await btn.click()
+    await expect(btn).toContainText('Clicks: 2')
+  })
+
+  test('Vuetify primary theme color resolves on rendered button', async ({ mount, page }) => {
+    await mount(SanityButtonHarness)
+
+    // Vuetify exposes theme primary as "R, G, B" decimals on
+    // --v-theme-primary (e.g. "31, 122, 209" for #1f7ad1).
+    const themePrimary = await page.evaluate(() => {
+      const root = document.documentElement
+
+      return getComputedStyle(root).getPropertyValue('--v-theme-primary').trim()
+    })
+
+    expect(themePrimary).not.toBe('')
+    expect(themePrimary.split(',')).toHaveLength(3)
+  })
+})