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

app/Http/Controllers/HelpController.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace App\Http\Controllers;
+
+use Illuminate\View\View;
+
+class HelpController extends Controller
+{
+    public function manual(): View
+    {
+        return view('help.manual');
+    }
+
+    public function changelog(): View
+    {
+        $changelogPath = base_path('CHANGELOG.md');
+        $content = file_exists($changelogPath)
+            ? file_get_contents($changelogPath)
+            : 'Kein Changelog gefunden.';
+
+        return view('help.changelog', compact('content'));
+    }
+}