Redesign SNS quick login buttons

Show Naver/Kakao/Google as circular icon buttons with a 'SNS 간편로그인' label, and toggle the group based on configured connections.

Co-authored-by: Cursor <cursoragent@cursor.com>

script.js

@@ -22,6 +22,7 @@
     userText: document.getElementById("userText"),
     btnLogin: document.getElementById("btnLogin"),
     btnLogout: document.getElementById("btnLogout"),
+    snsLogin: document.getElementById("snsLogin"),
     btnGoogle: document.getElementById("btnGoogle"),
     btnKakao: document.getElementById("btnKakao"),
     btnNaver: document.getElementById("btnNaver"),
@@ -463,6 +464,7 @@
     if (el.btnGoogle) el.btnGoogle.hidden = !g;
     if (el.btnKakao) el.btnKakao.hidden = !k;
     if (el.btnNaver) el.btnNaver.hidden = !n;
+    if (el.snsLogin) el.snsLogin.hidden = !(g || k || n);
   }
 
   function applyManageLock() {