Switch login to password-only and split pack zip paths

- Login form/route accepts password only; matched account row provides session userId
- PackDefinition: replace packPath with mapPath (.mc_custom/saves) and serverPath (server install dir); editor exposes two .zip fields
- Installer resolves relative platform/map/server URLs against manifest origin under /file/{platforms,maps,servers}/<name>; downloads and extracts the zips

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

views/op/login.ejs

@@ -13,13 +13,9 @@
       <p class="errorBanner"><%= error %></p>
     <% } %>
     <form method="post" action="/op" class="loginForm">
-      <label>
-        <span>아이디</span>
-        <input name="id" autocomplete="username" required autofocus />
-      </label>
       <label>
         <span>비밀번호</span>
-        <input name="password" type="password" autocomplete="current-password" required />
+        <input name="password" type="password" autocomplete="current-password" required autofocus />
       </label>
       <button class="primaryButton" type="submit">로그인</button>
     </form>