fix: target prod runner (runs-on: prod) instead of ubuntu-latest

Root cause: deploy.yml used runs-on: ubuntu-latest, which matched
the 4C4G web runner instead of the 8C32G prod runner. The web runner
doesn't have access to /opt/zhixi/, systemd, or Docker.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/deploy.yml

@@ -6,7 +6,7 @@ on:
 
 jobs:
   build-and-deploy:
-    runs-on: ubuntu-latest
+    runs-on: prod
     steps:
       - name: Checkout latest code
         run: |