⚡️(ci) shard e2e tests and cache playwright browsers

E2e tests take 20-23min per browser because they run sequentially
on a single runner with no browser caching. Shard tests across 3
parallel runners per browser and cache Playwright browser binaries
to reduce wall-clock time to ~7min per browser.

.github/workflows/drive-frontend.yml

@@ -66,11 +66,16 @@ jobs:
     runs-on: ubuntu-latest
     needs: [install-front, build-mails]
     strategy:
+      fail-fast: false
       matrix:
         browser:
           - chromium
           - webkit
           - firefox
+        shard:
+          - "1/3"
+          - "2/3"
+          - "3/3"
     steps:
       - name: Checkout repository
         uses: actions/checkout@v6
@@ -93,6 +98,13 @@ jobs:
           path: "src/backend/core/templates/mail"
           key: mail-templates-${{ hashFiles('src/mail/mjml') }}
 
+      - name: Cache Playwright browsers
+        id: playwright-cache
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/ms-playwright
+          key: playwright-${{ matrix.browser }}-${{ hashFiles('src/frontend/**/yarn.lock') }}
+
       - name: Install Playwright Browsers
         run: |
           cd src/frontend/apps/e2e
@@ -113,11 +125,11 @@ jobs:
       - name: Run e2e tests
         run: |
           cd src/frontend/apps/e2e
-          yarn test --project=${{ matrix.browser }}
+          yarn test --project=${{ matrix.browser }} --shard=${{ matrix.shard }}
 
       - uses: actions/upload-artifact@v4
         if: always()
         with:
-          name: report-${{ matrix.browser }}
+          name: report-${{ matrix.browser }}-shard-${{ strategy.job-index }}
           path: src/frontend/apps/e2e/report/
           retention-days: 7