Fix ISO build: use :latest tag (BlueBuild doesn't tag :vX.Y.Z)

BlueBuild tags images as :latest on main pushes, not :vX.Y.Z. The
release tag and main HEAD are the same commit, so :latest is the
correct image for ISO generation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: SecAI-Hub

.github/workflows/release.yml

@@ -167,7 +167,9 @@ jobs:
           arch: x86_64
           image_name: secai_os
           image_repo: ghcr.io/secai-hub
-          image_tag: ${{ github.ref_name }}
+          # Use :latest since BlueBuild tags main pushes as :latest, not :vX.Y.Z.
+          # The release tag and main HEAD point to the same commit.
+          image_tag: latest
           version: 42
           variant: Silverblue
           iso_name: secai-os-${{ github.ref_name }}-x86_64.iso