feat: Gitea CI workflow + registry image для деплоя

- .gitea/workflows/docker-build.yml: билд и пуш образа в Gitea Container Registry
- docker-compose.server.yml: убрал build context, используем registry image
- Требует REGISTRY_TOKEN секрет в настройках репо

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.gitea/workflows/docker-build.yml

@@ -0,0 +1,33 @@
+name: Build and Push Docker Image
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Clone repository
+        env:
+          GIT_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+        run: |
+          SERVER_HOST=$(echo "${{ gitea.server_url }}" | sed 's|https\?://||')
+          git clone --depth 2 "http://${{ gitea.actor }}:${GIT_TOKEN}@${SERVER_HOST}/${{ gitea.repository }}.git" .
+          git checkout ${{ gitea.sha }}
+
+      - name: Build and push image
+        run: |
+          REGISTRY_HOST=$(echo "${{ gitea.server_url }}" | sed 's|https\?://||')
+          IMAGE="${REGISTRY_HOST}/${{ gitea.repository }}/sing-proxy"
+
+          echo "${{ secrets.REGISTRY_TOKEN }}" | docker login "$REGISTRY_HOST" -u "${{ gitea.actor }}" --password-stdin
+
+          docker build \
+            -f docker/Dockerfile.singbox \
+            -t "${IMAGE}:latest" \
+            .
+
+          docker push "${IMAGE}:latest"
+          echo "Pushed: ${IMAGE}:latest"