fix(ci): use GitHub-hosted runners until self-hosted are deployed

All CI runs are stuck in queued — zero self-hosted runners are registered
for the groombook-runners label. Switch to ubuntu-latest to unblock PRs.

Tracked in groombook/infra#2 — will revert once self-hosted runners are
deployed to the cluster.

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

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ on:
 jobs:
   lint-typecheck:
     name: Lint & Typecheck
-    runs-on: groombook-runners
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
 
@@ -33,7 +33,7 @@ jobs:
 
   test:
     name: Test
-    runs-on: groombook-runners
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
 
@@ -54,7 +54,7 @@ jobs:
 
   build:
     name: Build
-    runs-on: groombook-runners
+    runs-on: ubuntu-latest
     needs: [lint-typecheck, test]
     steps:
       - uses: actions/checkout@v4
@@ -76,7 +76,7 @@ jobs:
 
   docker:
     name: Build Docker Images
-    runs-on: groombook-runners
+    runs-on: ubuntu-latest
     needs: [build]
     if: github.ref == 'refs/heads/main'
     steps: