Add social quick login and user sync API

Add quick provider login buttons (Auth0 connections), an API to upsert users into Postgres and gate admin via can_manage, plus schema and Node server.

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

index.html

@@ -71,6 +71,9 @@
             <span class="user-dot" aria-hidden="true"></span>
             <span class="user-text" id="userText">로그인 필요</span>
           </div>
+          <button class="btn" id="btnGoogle" type="button" hidden>구글</button>
+          <button class="btn" id="btnKakao" type="button" hidden>카카오</button>
+          <button class="btn" id="btnNaver" type="button" hidden>네이버</button>
           <button class="btn" id="btnLogin" type="button">로그인</button>
           <button class="btn" id="btnLogout" type="button" hidden>로그아웃</button>
         </div>
@@ -203,6 +206,14 @@
             <div class="hint">쉼표로 구분합니다. 비워두면 “로그인한 모든 계정”이 관리 가능해집니다.</div>
           </label>
 
+          <label class="field">
+            <span class="field-label">Connection 이름(선택)</span>
+            <input id="authConnGoogle" class="input" type="text" placeholder="Google 예: google-oauth2" />
+            <input id="authConnKakao" class="input" type="text" placeholder="Kakao 예: kakao" />
+            <input id="authConnNaver" class="input" type="text" placeholder="Naver 예: naver" />
+            <div class="hint">Auth0에서 설정한 connection 이름입니다. 비우면 “로그인” 버튼으로 통합 로그인 화면을 띄웁니다.</div>
+          </label>
+
           <div class="modal-foot">
             <button class="btn btn-ghost" type="button" id="btnAuthReset">초기화</button>
             <button class="btn btn-primary" type="submit" id="btnAuthSave">저장</button>