Erweiterte Features (2/2): Cleanup/DSGVO, Webhooks, REST-API, Backup, CI, Docker

- Auto-Cleanup/DSGVO: cron_cleanup.php (token-geschützt) löscht abgelaufene
  Voucher, Audit-Log, Login-Versuche und Reset-Tokens nach konfigurierbaren
  Fristen
- Webhooks: includes/Notifier.php (Slack/Teams/generisch), Auslösung bei
  Voucher-Erstellung (Web + API)
- REST-API: includes/ApiKey.php (SHA-256, Präfix-Lookup), api/bootstrap.php,
  api/vouchers.php (GET/POST), api/sites.php; admin/api_keys.php zur Verwaltung
- Config-Backup/Restore: admin/backup.php (JSON Export/Import, Cron-Token
  geschützt)
- admin/integrations.php: Trusted-Proxy, Webhook, Cleanup-Fristen
- CI: .github/workflows/ci.yml (php -l auf 7.4 & 8.2, lang-Validierung)
- Docker: Dockerfile, docker-compose.yml (MariaDB), entrypoint (config aus ENV),
  .dockerignore
- Nav + i18n (DE/EN) für alle neuen Admin-Seiten

.github/workflows/ci.yml

@@ -0,0 +1,34 @@
+name: CI
+
+on:
+  push:
+    branches: [ "**" ]
+  pull_request:
+
+jobs:
+  lint:
+    name: PHP Lint
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        php: [ "7.4", "8.2" ]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup PHP ${{ matrix.php }}
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          extensions: pdo, pdo_mysql, curl, mbstring, json
+          coverage: none
+
+      - name: Syntax check all PHP files
+        run: |
+          set -e
+          find . -name '*.git' -prune -o -name '*.php' -print | while read -r f; do
+            php -l "$f"
+          done
+
+      - name: Validate JSON language/migration assets
+        run: |
+          php -r 'foreach (glob("lang/*.php") as $f) { $a = require $f; if (!is_array($a)) { fwrite(STDERR, "Bad lang file: $f\n"); exit(1);} } echo "lang OK\n";'