refactor: 폐쇄망 환경을 위해 UI html의 외부 CDN(Tailwind, Google Fonts)을 로컬 정적 리소스로 완전 대체

dat-gateway/src/main/resources/static/chat.html

@@ -4,11 +4,13 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>AX HUB - ChatClient</title>
-    <script src="https://unpkg.com/@tailwindcss/browser@4"></script>
+    <script src="/lib/tailwindcss.js"></script>
     <script src="/vendor/marked.umd.js"></script>
-    <link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600&display=swap" rel="stylesheet">
     <style>
-        body { font-family: 'Inter', sans-serif; background-color: #0f1115; color: #e2e8f0; }
+        :root {
+            --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
+        }
+        body { font-family: var(--font-sans); background-color: #0f1115; color: #e2e8f0; }
         .scrollbar-hide::-webkit-scrollbar { display: none; }
         .scrollbar-hide { -ms-overflow-style: none; scrollbar-width: none; }