* Re-enable london-b's third-party apt repos from Ansible
The lunar -> noble upgrade disabled every third-party repo on london-b, so
tailscale, jellyfin and plex have been frozen since. The common role can now
manage deb822 repos and clean up stale source/keyring files per host, and
london-b uses it for tailscale, jellyfin and plex (now on repo.plex.tv with
the v2 key). The dead sonarr v3, mono, nvidia, datadog and PPA leftovers go.
* Drop the explanatory comments from the apt repo change
The .terraform.lock.hcl was gitignored while providers use floating
~> constraints, so every CI 'tofu init' resolved provider versions
fresh and could drift from what was tested locally, with no checksum
verification on the providers.
Track the lock file instead, with hashes for linux_amd64 (CI) plus
darwin_arm64/amd64 (local). Dependabot's terraform updates now surface
exact provider version bumps as reviewable, hash-pinned changes.
