feat: add admin-only git pull interface and remove auto-pull

- Add new `gitpull.php` page for manual git pull execution by administrators
- Remove automatic git pull on homepage visit to prevent unintended updates
- Include git pull link in admin navigation menu for easy access
- Secure interface with admin-only access and sudo credentials configuration

web/gitpull.php

@@ -0,0 +1,57 @@
+<?php
+require_once('./include/db_info.inc.php');
+require_once('./include/const.inc.php');
+require_once('./include/memcache.php');
+require_once('./include/setlang.php');
+
+// 仅允许管理员访问
+if (!isset($_SESSION[$OJ_NAME.'_'.'administrator'])) {
+    $view_errors = "Permission denied.";
+    require("template/".$OJ_TEMPLATE."/error.php");
+    exit(0);
+}
+
+// ====================================================
+// 请在下方填写 sudo 用户名和密码
+$SUDO_USER     = 'jieer';          // 填写拥有 sudo 权限的用户名
+$SUDO_PASSWORD = 'cmf[420;';       // 填写该用户的 sudo 密码
+// ====================================================
+
+$src_path = '/home/judge/src';
+$output = [];
+$return_code = -1;
+
+if ($_SERVER['REQUEST_METHOD'] === 'POST') {
+    $cmd = "echo " . escapeshellarg($SUDO_PASSWORD)
+         . " | sudo -S -u " . escapeshellarg($SUDO_USER)
+         . " git -C " . escapeshellarg($src_path)
+         . " pull 2>&1";
+    exec($cmd, $output, $return_code);
+}
+
+$show_title = "Git Pull - " . $OJ_NAME;
+require("template/".$OJ_TEMPLATE."/header.php");
+?>
+
+<div class="ui segment" style="margin-top:20px;">
+    <h2 class="ui header">
+        <i class="cloud download icon"></i>
+        <div class="content">服务器更新 <small style="font-size:0.6em; color:#888;">(git pull <?php echo htmlspecialchars($src_path); ?>)</small></div>
+    </h2>
+
+    <?php if ($_SERVER['REQUEST_METHOD'] === 'POST'): ?>
+        <div class="ui <?php echo $return_code === 0 ? 'success' : 'error'; ?> message">
+            <div class="header"><?php echo $return_code === 0 ? '更新成功' : '更新失败（返回码：' . $return_code . '）'; ?></div>
+            <pre style="margin-top:8px; white-space:pre-wrap; word-break:break-all;"><?php echo htmlspecialchars(implode("\n", $output)); ?></pre>
+        </div>
+    <?php endif; ?>
+
+    <form method="post" action="gitpull.php" style="margin-top:16px;">
+        <button type="submit" class="ui primary button">
+            <i class="refresh icon"></i> 立即执行 git pull
+        </button>
+        <a class="ui button" href="javascript:history.back()">返回</a>
+    </form>
+</div>
+
+<?php require("template/".$OJ_TEMPLATE."/footer.php"); ?>