Custom Bazzite DX NVIDIA (open) image: BlueBuild recipe, GHCR workflow, cosign setup

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/build.yml

@@ -0,0 +1,37 @@
+name: bluebuild
+on:
+  schedule:
+    - cron: "00 06 * * *" # daily rebuild pulls in base-image updates (self-updating)
+  push:
+    branches:
+      - main
+    paths-ignore:
+      - "**.md"
+  pull_request:
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  bluebuild:
+    name: Build Custom Image
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+      id-token: write
+    strategy:
+      fail-fast: false
+      matrix:
+        recipe:
+          - recipe.yml
+    steps:
+      - name: Build Custom Image
+        uses: blue-build/github-action@v1.12.0
+        with:
+          recipe: ${{ matrix.recipe }}
+          cosign_private_key: ${{ secrets.SIGNING_SECRET }}
+          registry_token: ${{ github.token }}
+          pull_request_number: ${{ github.event.number }}