ci: run the e2e tests in four shards

One job ran all 300+ tests with one worker, about 20 minutes. Four
jobs at once take a quarter each, still with one worker per job.

.github/workflows/test.yml

@@ -43,8 +43,14 @@ jobs:
         run: npm --prefix packages/mcp-server run build && npm --prefix packages/mcp-server run check-package
 
   e2e:
-    name: E2E Tests
+    # Four jobs at once, each with a quarter of the tests and one worker:
+    # the same conditions per test, about a quarter of the time
+    name: E2E Tests (${{ matrix.shard }}/4)
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        shard: [1, 2, 3, 4]
     steps:
       - uses: actions/checkout@v6
 
@@ -76,7 +82,7 @@ jobs:
         run: npm run build
 
       - name: Run E2E tests
-        run: npm run test:e2e
+        run: npm run test:e2e -- --shard=${{ matrix.shard }}/4
         env:
           CI: true
 
@@ -84,6 +90,6 @@ jobs:
         uses: actions/upload-artifact@v6
         if: always()
         with:
-          name: playwright-report
+          name: playwright-report-${{ matrix.shard }}
           path: playwright-report/
           retention-days: 7