docs(contributing): fix branch refs and build steps, add PR template

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,27 @@
+## Description
+
+<!-- What does this PR do? Why is it needed? -->
+
+## Related Issues
+
+<!-- Link related issues, e.g. "Fixes #123" -->
+
+## Type of Change
+
+- [ ] Bug fix
+- [ ] New feature
+- [ ] Refactor (no functional change)
+- [ ] Documentation
+- [ ] Other (describe below)
+
+## Checklist
+
+- [ ] Code follows project conventions
+- [ ] `flutter analyze` and `flutter test` pass
+- [ ] `go vet ./...` and `go test ./...` pass in `go_backend/` (if Go code changed)
+- [ ] Documentation updated (if needed)
+- [ ] Commit messages follow the [conventional commits](https://www.conventionalcommits.org) format
+
+## Screenshots
+
+<!-- For UI changes, add before/after screenshots. Delete this section otherwise. -->