ci: use Playwright container image instead of downloading browsers

Run E2E tests inside mcr.microsoft.com/playwright container which has
Chromium pre-installed, eliminating the ~30s browser download on each run.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -62,6 +62,8 @@ jobs:
   e2e-tests:
     name: E2E Tests
     runs-on: ubuntu-latest
+    container:
+      image: mcr.microsoft.com/playwright:v1.58.0-noble
     steps:
       - uses: actions/checkout@v4
 
@@ -76,21 +78,6 @@ jobs:
 
       - run: pnpm install --frozen-lockfile
 
-      - name: Cache Playwright Browsers
-        id: playwright-cache
-        uses: actions/cache@v4
-        with:
-          path: ~/.cache/ms-playwright
-          key: playwright-${{ runner.os }}-${{ hashFiles('pnpm-lock.yaml') }}
-
-      - name: Install Playwright Browsers
-        if: steps.playwright-cache.outputs.cache-hit != 'true'
-        run: npx playwright install --with-deps chromium
-
-      - name: Install Playwright System Dependencies
-        if: steps.playwright-cache.outputs.cache-hit == 'true'
-        run: npx playwright install-deps chromium
-
       - name: Build (with coverage instrumentation)
         run: pnpm build
         env:
@@ -102,6 +89,7 @@ jobs:
         env:
           CI: true
           VITE_COVERAGE: 'true'
+          HOME: /root
 
       - name: Merge E2E coverage
         if: always()