feat: add common utilities and feedback handling scripts

- Introduced common.js for shared functions including API calls, error reporting, and UI helpers.
- Implemented feedback.js for the feedback reporting page, including form handling and displaying feedback status.
- Added layout.js for managing galaxy and section layouts in the visualization.
- Created login.js for user authentication with session management.
- Developed search.js for term searching based on user input and synonyms.
- Implemented signup.js for user registration with validation and immediate login.

web/admin.html

@@ -0,0 +1,52 @@
+<!doctype html>
+<html lang="ko">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>관리 · 지역사회간호학 개념 우주</title>
+  <meta name="robots" content="noindex">
+  <link rel="icon" href="/static/favicon.svg" type="image/svg+xml">
+  <link rel="stylesheet" href="/static/css/base.css">
+  <link rel="stylesheet" href="/static/css/admin.css">
+</head>
+<body>
+  <a class="skip-link" href="#view">본문으로 건너뛰기</a>
+  <header class="topbar" id="topbar">
+    <a class="brand" href="/">
+      <span class="brand-logo" aria-hidden="true"></span>
+      <span>
+        <span class="brand-title">지역사회간호학 개념 우주</span><br>
+        <span class="brand-sub">교과서 색인으로 만든 개념 지도</span>
+      </span>
+    </a>
+    <nav class="topnav" aria-label="주 메뉴">
+      <a href="/">개념 우주</a>
+      <a href="/feedback">오류 신고</a>
+      <a href="/admin" aria-current="page">관리</a>
+    </nav>
+    <div class="who" id="who" hidden>
+      <span class="who-name" id="who-name"></span>
+      <button type="button" class="btn small ghost" id="logout">로그아웃</button>
+    </div>
+  </header>
+
+  <!-- 관리 화면 -->
+  <div id="app-view" hidden>
+    <nav class="tabs" id="tabs" aria-label="관리 메뉴">
+      <a href="#dashboard" data-tab="dashboard">대시보드</a>
+      <a href="#feedback" data-tab="feedback">피드백 <span class="count" id="tab-fb-count" hidden></span></a>
+      <a href="#terms" data-tab="terms">용어</a>
+      <a href="#relations" data-tab="relations">관계</a>
+      <a href="#questions" data-tab="questions">문제</a>
+      <a href="#codes" data-tab="codes">가입 코드</a>
+      <a href="#members" data-tab="members">회원 관리 <span class="count" id="tab-mem-count" hidden></span></a>
+      <a href="#structure" data-tab="structure">은하·단원</a>
+      <a href="#settings" data-tab="settings">설정</a>
+      <a href="#audit" data-tab="audit">기록</a>
+    </nav>
+    <main id="view" class="view" tabindex="-1"></main>
+  </div>
+
+  <script type="module" src="/static/js/admin.js"></script>
+</body>
+</html>