System plugin support: admin menu items, admin routes, API integration

- PluginManager: getAdminMenuItems(), handleAdminRoute(), getPluginType()
- admin.php: load PluginManager, pass plugin_admin_menu to Twig
- admin.php: route to plugin admin pages via handleAdminRoute()
- admin.twig: show 'Plugins' sidebar section for system plugins
- plugins-new.twig: choose content or system plugin type
- handlePluginsNew: generate proper template based on type (content/system)
- plugin-admin.twig: renders plugin output in admin layout
- GeoIPInfo: example system plugin (admin page with GeoIP info)
- System plugins: getAdminMenu(), getAdminRoutes(), handleAdminRoute()
- Content plugins: getSidebarContent() (unchanged)

plugins/GeoIPInfo/GeoIPInfo.php

@@ -0,0 +1,57 @@
+<?php
+
+class GeoIPInfo
+{
+    private ?CMSAPI $api = null;
+
+    public function setAPI(CMSAPI $api): void
+    {
+        $this->api = $api;
+    }
+
+    public function getConfig(): array
+    {
+        return [
+            'title' => 'GeoIP Info',
+            'type' => 'system',
+        ];
+    }
+
+    /**
+     * Register admin menu items.
+     */
+    public function getAdminMenu(): array
+    {
+        return [
+            ['label' => 'GeoIP Info', 'route' => 'geoip-info', 'icon' => 'bi-globe2'],
+        ];
+    }
+
+    /**
+     * Register admin routes this plugin handles.
+     */
+    public function getAdminRoutes(): array
+    {
+        return ['geoip-info'];
+    }
+
+    /**
+     * Handle admin route — render the admin page.
+     */
+    public function handleAdminRoute(string $route): void
+    {
+        $ip = $_SERVER['REMOTE_ADDR'] ?? '127.0.0.1';
+        $geoip = new GeoIP();
+        $countryCode = $geoip->lookupCountry($ip);
+        $country = GeoIP::getCountryName($countryCode);
+        $flag = GeoIP::getCountryFlagEmoji($countryCode);
+
+        echo '<h2 class="mb-4"><i class="bi bi-globe2"></i> GeoIP Info</h2>';
+        echo '<div class="card shadow-sm"><div class="card-body">';
+        echo '<table class="table table-sm">';
+        echo '<tr><td>IP adres</td><td><code>' . htmlspecialchars($ip) . '</code></td></tr>';
+        echo '<tr><td>Land</td><td>' . $flag . ' ' . htmlspecialchars($country) . '</td></tr>';
+        echo '</table>';
+        echo '</div></div>';
+    }
+}