ci: add PR build check workflow and PR template

- Add build.yml workflow that runs npm run build on PRs to main/dev
- Add PR template with summary, type, changes, test plan sections
- Required by branch protection rules on main

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

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,31 @@
+## Summary
+
+<!-- Briefly describe what this PR does and why -->
+
+## Type of Change
+
+- [ ] Feature (new functionality)
+- [ ] Bug fix
+- [ ] Refactor (no functional change)
+- [ ] Docs
+- [ ] CI/CD
+- [ ] Other
+
+## Changes
+
+<!-- List the key changes made -->
+
+## Test Plan
+
+<!-- How did you test? What should reviewers verify? -->
+
+- [ ] Build passes (`npm run build`)
+- [ ] Tested manually
+
+## Screenshots (if applicable)
+
+<!-- Add screenshots for UI changes -->
+
+## Related Issues
+
+<!-- Link related issues, e.g. Closes #123 -->