ci: Renovate opens version bump PRs with release notes

Versions are pinned across the Ansible vars, compose files, Terraform
providers and workflows, and nothing says when one is behind. Run
Renovate daily from Forgejo Actions: one PR per available bump, with
the upstream changelog in the body, which the deploy pipeline then
dry-runs like any other branch.

Variables are tracked through a "# renovate: datasource=... depName=..."
comment above them; Forgejo, Traefik, the runner and its nix image get
one here. The Paper JRE tag is left alone, the runner and nix bumps
carry their manual follow-up steps in the PR, and Renovate's own image
is bumped monthly.

Needs the repository secrets RENOVATE_TOKEN (bot user with write
access) and GH_COM_TOKEN (read-only github.com token for release
notes).

Assisted-by: Claude:opus-5-5

ansible/inventory/group_vars/services_servers/forgejo_runner.yaml

@@ -2,6 +2,7 @@
 # Forgejo Runner (CI/CD) configuration
 
 # Runner version and settings
+# renovate: datasource=docker depName=code.forgejo.org/forgejo/runner
 forgejo_runner_version: "11"
 forgejo_runner_capacity: 4
 forgejo_runner_timeout: 3h
@@ -10,6 +11,7 @@ forgejo_runner_timeout: 3h
 # /nix, seeded from this image on first use; the image's /bin/sh and
 # /etc/nix/nix.conf link into that store, so a volume from another
 # version breaks them. Bumping this also switches to a fresh volume.
+# renovate: datasource=docker depName=nixos/nix
 forgejo_runner_nix_version: "2.35.3"
 forgejo_runner_token: "{{ vault_forgejo_runner_token }}"