Fix SQLite backtick translation, add service-switch SSE streaming, Fail2Ban management page

- DB.php: fix backtick-quoted column names in ON DUPLICATE KEY UPDATE VALUES() regex
- DB.php: add global backtick→double-quote identifier strip
- system.php: add service-switch SSE streaming endpoint for web/mail/ftp/dns server changes
- system.php: simplify save-option to DB save only (no inline shell)
- firewall.php: add f2b-config-get, f2b-config-save, f2b-log, f2b-jail, f2b-ban, f2b-unban, f2b-ignoreip-* actions
- admin.js: Fail2Ban dedicated management page with jail table, global settings, whitelist, log viewer
- admin.js: soSave() now uses streaming terminal overlay instead of blocking spinner
- admin/index.php: split Firewall (UFW) and Fail2Ban into separate sidebar entries

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

panel/public/admin/index.php

@@ -113,7 +113,11 @@ require_once dirname(__DIR__) . '/_branding.php';
         </a>
         <a href="#" class="sidebar-link" data-page="firewall">
           <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><rect x="3" y="11" width="18" height="11" rx="2" ry="2"/><path d="M7 11V7a5 5 0 0 1 10 0v4"/></svg>
-          Firewall / Fail2Ban
+          Firewall (UFW)
+        </a>
+        <a href="#" class="sidebar-link" data-page="fail2ban">
+          <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M12 22s8-4 8-10V5l-8-3-8 3v7c0 6 8 10 8 10z"/><line x1="12" y1="8" x2="12" y2="12"/><line x1="12" y1="16" x2="12.01" y2="16"/></svg>
+          Fail2Ban
         </a>
         <a href="#" class="sidebar-link" data-page="audit-log">
           <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M14 2H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V8z"/><polyline points="14 2 14 8 20 8"/><line x1="16" y1="13" x2="8" y2="13"/><line x1="16" y1="17" x2="8" y2="17"/><polyline points="10 9 9 9 8 9"/></svg>