add CI smoke workflow

.gitea/workflows/ci.yml

@@ -0,0 +1,17 @@
+name: CI Smoke Test
+on:
+  push:
+    branches: [main]
+jobs:
+  smoke:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Hello
+        run: echo "Runner is alive on host $(hostname)"
+      - name: Docker available (DinD)
+        run: |
+          docker version
+          echo "FROM alpine:3.20" > Dockerfile
+          echo "RUN echo built-by-vv-runner > /built.txt" >> Dockerfile
+          docker build -t vv-ci-smoke:test .
+          docker run --rm vv-ci-smoke:test cat /built.txt