fix: skip Docker build on Gitea runner (no Docker installed)

.github/workflows/build.yaml

@@ -10,6 +10,8 @@ env:
 
 jobs:
   build:
+    # Skip on Gitea - runner lacks Docker
+    if: ${{ !env.GITEA_ACTIONS }}
     runs-on: ubuntu-latest
     permissions:
       contents: read