Update legal documents and localization for compliance and clarity

- Updated .env.example with legal operator details for compliance.
- Refactored Impressum, Privacy, and Terms pages to utilize a new LegalDocument component for improved structure and maintainability.
- Enhanced localization files to include legal content in both German and English, ensuring accurate representation of legal information.
- Improved i18n handling to support locale detection from Accept-Language headers.

landingpage/includes/bootstrap.php

@@ -0,0 +1,77 @@
+<?php
+declare(strict_types=1);
+
+$config = require dirname(__DIR__) . '/config.php';
+
+function h(?string $value): string
+{
+    return htmlspecialchars((string) $value, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8');
+}
+
+/**
+ * @return 'de'|'en'
+ */
+function detect_locale(): string
+{
+    if (isset($_GET['lang']) && ($_GET['lang'] === 'de' || $_GET['lang'] === 'en')) {
+        return $_GET['lang'];
+    }
+
+    $header = $_SERVER['HTTP_ACCEPT_LANGUAGE'] ?? '';
+    if ($header === '') {
+        return 'de';
+    }
+
+    $preferred = [];
+    foreach (explode(',', $header) as $part) {
+        $part = trim($part);
+        if ($part === '') {
+            continue;
+        }
+        [$tag, $q] = array_pad(explode(';q=', $part, 2), 2, '1');
+        $lang = strtolower(substr(trim($tag), 0, 2));
+        $preferred[$lang] = (float) $q;
+    }
+
+    arsort($preferred);
+    foreach (array_keys($preferred) as $lang) {
+        if ($lang === 'de' || $lang === 'en') {
+            return $lang;
+        }
+    }
+
+    return 'de';
+}
+
+/**
+ * @return array<string, mixed>
+ */
+function load_messages(string $locale): array
+{
+    $path = dirname(__DIR__) . '/lang/' . $locale . '.php';
+    /** @var array<string, mixed> $messages */
+    $messages = require $path;
+    return $messages;
+}
+
+function t(array $messages, string $key, ?string $fallback = null): string
+{
+    $parts = explode('.', $key);
+    $value = $messages;
+    foreach ($parts as $part) {
+        if (!is_array($value) || !array_key_exists($part, $value)) {
+            return $fallback ?? $key;
+        }
+        $value = $value[$part];
+    }
+    return is_string($value) ? $value : ($fallback ?? $key);
+}
+
+function bot_invite_url(array $config): string
+{
+    return 'https://discord.com/api/oauth2/authorize?' . http_build_query([
+        'client_id' => (string) $config['bot_client_id'],
+        'permissions' => '8',
+        'scope' => 'bot applications.commands',
+    ], '', '&', PHP_QUERY_RFC3986);
+}