fix: remove environment.yml push trigger from cache workflow (#34)

In container mode, environment.yml has no effect on the build — the
container's pre-installed environment is used. No need to trigger a
cache rebuild when this file changes. The weekly schedule handles
regular cache refreshes.

Add artifact upload to cache workflow for visibility

Add packages:read permission for container access

Tag-triggered workflows may need explicit package permission to pull
from GHCR.

Add packages:read permission for container access

Tag-triggered workflows may need explicit package permission to pull
from GHCR.

Add packages:read permission for container access

Tag-triggered workflows may need explicit package permission to pull
from GHCR.

Add packages:read permission for container access

Tag-triggered workflows may need explicit package permission to pull
from GHCR.

Update README.md

Disable notebook syncing for testing