feat(ci): add registry cleanup script

Cleans everything older than 90 days.

.github/workflows/clean.yml

@@ -0,0 +1,23 @@
+name: Cleanup Old Images
+on:
+  schedule:
+    - cron: "15 0 * * 0" # 0015 UTC on Sundays
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref || github.run_id }}
+
+jobs:
+  delete-older-than-90:
+    runs-on: ubuntu-latest
+    permissions:
+      packages: write
+    steps:
+      - name: Delete Images Older Than 90 Days
+        uses: dataaxiom/[email protected]
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          packages: silverblue-main, kinoite-main, sericea-main, onyx-main, base-main, lazurite-main, vauxite-main          older-than: 90 days
+          delete-orphaned-images: true
+          keep-n-tagged: 7
+          keep-n-untagged: 7