Add full-stack Hello World app with CI/CD

- Go backend with PostgreSQL connection
- Next.js frontend with TypeScript
- Docker Compose for local development
- Woodpecker CI pipeline for build and push
- Kubernetes manifests with Kustomize
- ArgoCD application for GitOps deployment

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/app/page.tsx

@@ -0,0 +1,118 @@
+'use client'
+
+import { useEffect, useState } from 'react'
+
+interface ApiResponse {
+  message: string
+  db_status: string
+}
+
+export default function Home() {
+  const [data, setData] = useState<ApiResponse | null>(null)
+  const [loading, setLoading] = useState(true)
+  const [error, setError] = useState<string | null>(null)
+
+  useEffect(() => {
+    const apiUrl = process.env.NEXT_PUBLIC_API_URL || 'http://localhost:8080'
+
+    fetch(`${apiUrl}/api/hello`)
+      .then((res) => res.json())
+      .then((data) => {
+        setData(data)
+        setLoading(false)
+      })
+      .catch((err) => {
+        setError(err.message)
+        setLoading(false)
+      })
+  }, [])
+
+  return (
+    <main style={styles.main}>
+      <div style={styles.container}>
+        <h1 style={styles.title}>Hello World!</h1>
+        <p style={styles.subtitle}>Go + PostgreSQL + Next.js</p>
+
+        <div style={styles.card}>
+          {loading && <p>Loading...</p>}
+          {error && <p style={styles.error}>Error: {error}</p>}
+          {data && (
+            <>
+              <p style={styles.message}>{data.message}</p>
+              <p style={styles.status}>
+                Database:
+                <span style={{
+                  color: data.db_status === 'connected' ? '#22c55e' : '#ef4444',
+                  marginLeft: '8px'
+                }}>
+                  {data.db_status}
+                </span>
+              </p>
+            </>
+          )}
+        </div>
+
+        <div style={styles.techStack}>
+          <span style={styles.badge}>Go</span>
+          <span style={styles.badge}>PostgreSQL</span>
+          <span style={styles.badge}>Next.js</span>
+        </div>
+      </div>
+    </main>
+  )
+}
+
+const styles: { [key: string]: React.CSSProperties } = {
+  main: {
+    minHeight: '100vh',
+    display: 'flex',
+    alignItems: 'center',
+    justifyContent: 'center',
+    background: 'linear-gradient(135deg, #667eea 0%, #764ba2 100%)',
+    fontFamily: 'system-ui, -apple-system, sans-serif',
+  },
+  container: {
+    textAlign: 'center',
+    color: 'white',
+  },
+  title: {
+    fontSize: '4rem',
+    marginBottom: '0.5rem',
+    textShadow: '2px 2px 4px rgba(0,0,0,0.2)',
+  },
+  subtitle: {
+    fontSize: '1.25rem',
+    opacity: 0.9,
+    marginBottom: '2rem',
+  },
+  card: {
+    background: 'rgba(255,255,255,0.95)',
+    borderRadius: '12px',
+    padding: '2rem',
+    color: '#333',
+    boxShadow: '0 10px 40px rgba(0,0,0,0.2)',
+    marginBottom: '2rem',
+  },
+  message: {
+    fontSize: '1.25rem',
+    fontWeight: 500,
+  },
+  status: {
+    marginTop: '1rem',
+    fontSize: '1rem',
+  },
+  error: {
+    color: '#ef4444',
+  },
+  techStack: {
+    display: 'flex',
+    gap: '1rem',
+    justifyContent: 'center',
+  },
+  badge: {
+    background: 'rgba(255,255,255,0.2)',
+    padding: '0.5rem 1rem',
+    borderRadius: '20px',
+    fontSize: '0.875rem',
+  },
+}