feat: downgrade tech stack to stable versions and integrate GA4 error monitoring

- Downgrade Next.js 16→14.2, React 19→18.3, Tailwind 4→3.4
- Add comprehensive GA4 error monitoring system
- Create Jenkins CI/CD pipeline with quality gates
- Fix build issues: ESLint, SWC conflict, config format
- Add documentation for deployment and error tracking

sentry.edge.config.ts

@@ -0,0 +1,15 @@
+import * as Sentry from '@sentry/nextjs';
+
+const SENTRY_DSN = process.env.SENTRY_DSN || '';
+
+if (SENTRY_DSN) {
+  Sentry.init({
+    dsn: SENTRY_DSN,
+    environment: process.env.NODE_ENV || 'development',
+    enabled: process.env.NODE_ENV !== 'development',
+
+    tracesSampleRate: 1.0,
+  });
+}
+
+export default Sentry;