stem95su: scheduled Drive->site sync CronJob (every 10m)

CronJob stem95su-gdrive-sync (*/10) mounts the content PVC RW and
rclone-syncs the read-only Drive folder "claude" (stem claude/files) onto
it (rclone/rclone:1.74.3, scope=drive.readonly, empty-source guard +
--max-delete 25). ESO ExternalSecret stem95su-rclone <- Vault
secret/stem95su. Requires the GCP OAuth app published to Production or the
refresh token expires ~weekly.

Lands the gdrive-sync stack on master (it had landed on a feature branch
by accident on the shared devvm checkout).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/build-diun.yml

@@ -1,28 +0,0 @@
-name: Build Custom DIUN Image
-
-on:
-  push:
-    branches: [master]
-    paths:
-      - 'stacks/diun/Dockerfile'
-  workflow_dispatch:
-
-jobs:
-  build:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-
-      - uses: docker/setup-buildx-action@v3
-
-      - uses: docker/login-action@v3
-        with:
-          username: ${{ secrets.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_TOKEN }}
-
-      - uses: docker/build-push-action@v6
-        with:
-          context: stacks/diun
-          platforms: linux/amd64
-          push: true
-          tags: viktorbarzin/diun:latest