feat(layout): Layout-Einstellungen, Dark-Mode, Logo, Hilfe-Menü

- Settings Key-Value Store (DB + Cache)
- Einstellungen → Layout: Seitenname, Logo, Button-Farbe, Dark/Light-Mode
- Hilfe-Menü (Ebene 0): Handbuch + Changelog im Browser
- Navigation erweitert: Einstellungen-Dropdown + Hilfe-Dropdown
- CHANGELOG v0.4.0

Version: 0.4.0

database/seeders/SettingsSeeder.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Database\Seeders;
+
+use App\Models\Setting;
+use Illuminate\Database\Seeder;
+
+class SettingsSeeder extends Seeder
+{
+    public function run(): void
+    {
+        $defaults = [
+            'site_name'      => 'Network-MGMT',
+            'site_logo'      => '',
+            'button_color'   => '#4f46e5',  // Indigo-600
+            'theme_mode'     => 'light',    // light | dark
+        ];
+
+        foreach ($defaults as $key => $value) {
+            Setting::firstOrCreate(['key' => $key], ['value' => $value]);
+        }
+
+        $this->command->info('Default settings seeded.');
+    }
+}