ci: extend smoke workflow with a real Linux build job

.gitea/workflows/smoke.yml

@@ -1,8 +1,8 @@
-# Gitea Actions smoke test for the self-hosted Windows runner (RARE-win).
+# Gitea Actions smoke test for the self-hosted runners.
 # Deliberately uses NO `uses:` steps: Gitea resolves actions from
 # data.forgejo.org, which does not carry actions/checkout@v6 or
 # actions/setup-dotnet@v4, so the .github workflows cannot run here as-is.
-# This proves runner execution independently of that.
+# Checkout is therefore done with plain git against the same instance.
 name: smoke
 on:
   workflow_dispatch:
@@ -11,11 +11,25 @@ jobs:
   windows-smoke:
     runs-on: windows-latest
     steps:
-      - name: Report the build environment
+      - name: Environment
         shell: pwsh
         run: |
-          Write-Host "host   : $env:COMPUTERNAME"
+          Write-Host "host=$env:COMPUTERNAME user=$env:USERNAME cores=$env:NUMBER_OF_PROCESSORS"
-          Write-Host "user   : $env:USERNAME"
-          Write-Host "cores  : $env:NUMBER_OF_PROCESSORS"
           dotnet --list-sdks
           git --version
+
+  linux-build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Environment
+        run: |
+          echo "host=$(hostname) user=$(whoami) cores=$(nproc)"
+          dotnet --list-sdks
+          git --version
+      - name: Clone and build a real project
+        run: |
+          set -e
+          rm -rf src-smoke
+          git clone --depth 1 https://git.snakedesert.se/erik/acdream.git src-smoke
+          cd src-smoke
+          dotnet build src/AcDream.Launcher.Core/AcDream.Launcher.Core.csproj -c Release --nologo