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/login.html

@@ -0,0 +1,27 @@
+<!doctype html>
+<html lang="ko">
+<head>
+<meta charset="utf-8">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<title>로그인 · 지역사회간호학 개념 우주</title>
+<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/account.css">
+<script type="module" src="/static/js/login.js"></script>
+</head>
+<body>
+<header class="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="주요 메뉴">
+    <a href="/">개념 우주</a>
+    <a href="/feedback">오류 신고</a>
+    <a href="/login" aria-current="page">로그인</a>
+    <a href="/signup">회원 가입</a>
+  </nav>
+</header>
+<main class="auth-wrap" id="main"></main>
+</body>
+</html>