Add Gitea Actions deploy workflow and server configuration

- Add basePath /admin to Next.js config for path-based routing
- Add .gitea/workflows/deploy.yml for CI/CD via Gitea Actions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/deploy.yml

@@ -0,0 +1,29 @@
+name: Deploy to Server
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Build API image
+        run: |
+          docker build -t rustycms-api:latest .
+
+      - name: Build Admin UI image
+        run: |
+          docker build \
+            --build-arg NEXT_PUBLIC_RUSTYCMS_API_URL=https://cms.pm86.de \
+            -t rustycms-admin:latest \
+            ./admin-ui
+
+      - name: Deploy
+        run: |
+          docker compose -f /opt/rustycms/docker-compose.yml up -d
+          docker image prune -f