fix(ci): use self-hosted runners for E2E job

Change E2E job runs-on from ubuntu-latest to runners-groombook
per org policy. Unblocks Playwright E2E tests (GRO-77).

Closes #80

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

.github/workflows/ci.yml

@@ -50,7 +50,7 @@ jobs:
 
   e2e:
     name: E2E Tests
-    runs-on: ubuntu-latest
+    runs-on: runners-groombook
     needs: [lint-typecheck, test]
     steps:
       - uses: actions/checkout@v4