fix: convert GitHub Pages workflow to CI-only

The workflow was failing because upload-pages-artifact expected a dist/
directory that doesn't exist — this project deploys to Vercel, not
GitHub Pages. Remove Pages deployment steps and keep lint/test/build
as CI quality gates. Also add PR trigger.

Author: kevinkiklee

.github/workflows/deploy.yml

@@ -1,24 +1,18 @@
-name: Deploy to GitHub Pages
+name: CI
 
 on:
   push:
     branches: [main]
-
-permissions:
-  contents: read
-  pages: write
-  id-token: write
+  pull_request:
+    branches: [main]
 
 concurrency:
-  group: pages
+  group: ci-${{ github.ref }}
   cancel-in-progress: true
 
 jobs:
-  build-and-deploy:
+  build:
     runs-on: ubuntu-latest
-    environment:
-      name: github-pages
-      url: ${{ steps.deployment.outputs.page_url }}
     steps:
       - uses: actions/checkout@v5
 
@@ -32,11 +26,3 @@ jobs:
       - run: npm run lint
       - run: npm test
       - run: npm run build
-
-      - uses: actions/configure-pages@v5
-      - uses: actions/upload-pages-artifact@v4
-        with:
-          path: dist
-
-      - id: deployment
-        uses: actions/deploy-pages@v5