feat(build): add backend-focused testing commands

- Add 'make full-check-backend' for fast backend testing without E2E
- Add 'make test-backend' for unit and integration tests only
- Update 'test:integration' to use Jest instead of bun for consistency
- Improve command descriptions for clarity
- Enable fast development workflow by skipping E2E tests when not needed

package.json

@@ -16,7 +16,7 @@
     "test": "jest",
     "test:watch": "jest --watch",
     "test:coverage": "jest --coverage",
-    "test:integration": "bun tests/integration/production.test.js",
+    "test:integration": "jest tests/integration/production.test.js",
     "test:e2e": "playwright test",
     "test:e2e:ui": "playwright test --ui",
     "test:e2e:debug": "playwright test --debug",