Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/5051

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Roles affected: appservice-discord, appservice-irc, beeper-linkedin,
heisenbridge, hookshot, mautrix-bluesky, mautrix-discord,
mautrix-gmessages, mautrix-googlechat, mautrix-signal, mautrix-slack,
mautrix-twitter, mautrix-whatsapp, mautrix-wsproxy, mx-puppet-groupme,
mx-puppet-steam, postmoogle, sms, steam, cactus-comments, element,
fluffychat, schildichat, conduit, corporal, dendrite,
ldap-registration-proxy, media-repo, pantalaimon,
prometheus-nginxlog-exporter, registration, sygnal, synapse-admin,
user-verification-service.

For each role: renamed _docker_image* variables to _container_image*
(and _docker_src_files_path to _container_src_files_path where
applicable), added deprecation entries in validate_config.yml, and
updated group_vars/docs references.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

For each of the 34 roles (3 clients, 9 bots, 22 bridges), this commit:
- Adds `_restart_necessary: false` default variable
- Adds `register:` directives to config/image/systemd tasks
- Computes `_restart_necessary` via set_fact (OR of all .changed results)
- Wires `(_restart_necessary | bool)` in group_vars/matrix_servers

This allows the systemd service manager to skip unnecessary restarts
when running install-* tags and nothing actually changed.

Service roles and complex multi-service roles will follow separately.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/4776

Supersedes https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/4777

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/4445

This commit adds copyright attributions in SPDX to the files for matrix-client-fluffychat, following REUSE's specification.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

This:

- brings consistency - no more mixing `_name_prefix` and `_registry_prefix`
- adds extensibility - a future patch will allow reconfiguring all registry prefixes for all roles in the playbook

We still have `_docker_` vs `_container_` inconsistencies.
These may be worked on later.

* add FluffyChat

* capitalization

* Update group_vars/matrix_servers

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

* fix link in readme

---------

Co-authored-by: Slavi Pantaleev <slavi@devture.com>