feat(ci): Add arm64 emulation and multi-arch kernel build support

Introduce arm64 emulation setup and enhance the kernel build workflow to
support multi-architecture builds. Updated the process to use Docker
copy commands for compatibility with docker-in-docker environments, ensuring
accurate context access and successful compilation.

.gitea/workflows/build-kernel.yml

@@ -71,7 +71,7 @@ jobs:
           mv iec_listener.ko "out/modules/iec_listener_${safe}.ko"
 
       - name: Upload build output
-        uses: actions/upload-artifact@v4
+        uses: https://github.com/christopherHX/gitea-upload-artifact@v4
         with:
           # Name by the path-friendly version so artifact names stay unique; all
           # of them merge back into the single modules/ folder at download time.