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/index.php

@@ -3,14 +3,6 @@
 $cache_time = 30;
 $OJ_CACHE_SHARE = false;
 
-// Auto git pull on homepage visit (at most once per 60 seconds)
-$git_pull_lock = '/tmp/hustoj_git_pull.lock';
-if (!file_exists($git_pull_lock) || (time() - filemtime($git_pull_lock)) > 60) {
-    touch($git_pull_lock);
-    $repo_dir = dirname(__DIR__);
-    exec("cd " . escapeshellarg($repo_dir) . " && git pull > /tmp/hustoj_git_pull.log 2>&1 &");
-}
-
 require_once( './include/cache_start.php' );
 require_once( './include/db_info.inc.php' );
 require_once( './include/memcache.php' );