更新生产部署配置，调整工作流以支持 prod 分支，移除不再使用的数据库网络变量，并优化文档说明

.gitea/workflows/deploy-production.yaml

@@ -1,13 +1,15 @@
 name: Deploy production
 on:
   push:
-    branches: [main]
+    branches: [prod]
   workflow_dispatch:
 
 jobs:
   deploy:
-    # Reuse the runner that deploys zhixing-system to the same Docker host.
-    runs-on: ubuntu-latest
+    # Manual runs must also select prod before receiving production credentials.
+    if: ${{ github.ref == 'refs/heads/prod' }}
+    # Match the label of tencent-prod-runner on server B, not its runner name.
+    runs-on: tencent-prod
     steps:
       - name: Checkout
         uses: https://github.com/actions/checkout@v4
@@ -22,7 +24,6 @@ jobs:
           WQ_PASSWORD: ${{ secrets.WQ_PASSWORD }}
           ENCRYPTION_KEY: ${{ secrets.ENCRYPTION_KEY }}
           ADMIN_USERNAME: ${{ vars.ADMIN_USERNAME }}
-          DATABASE_NETWORK: ${{ vars.DATABASE_NETWORK }}
           PUBLIC_ORIGIN: ${{ vars.PUBLIC_ORIGIN }}
           MCP_ENABLED: ${{ vars.MCP_ENABLED }}
         run: bash scripts/deploy-production.sh