Replaces `community.docker.docker_image` with the modern
`docker_image_pull` and `docker_image_build` split modules across all
four task files (synapse, reverse_proxy_companion, goofys,
rust-synapse-compress-state). Drops the `ansible_version` compatibility
ladder and removes four `_container_image_force_pull` variables (the new
pull module handles registry refresh natively via `pull: always`).

The Synapse self-build path uses `ansible.builtin.shell` for BuildKit
support and is left as-is. The customizations image build (which builds
on top of the locally-tagged synapse image) is converted to
`docker_image_build` with `pull: false`, preserving its existing
rebuild-trigger semantics.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/5191.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

The companion role was tightly coupled to Synapse through shared tags, worker routing, and lifecycle ordering. Keeping them separate added coordination overhead without practical benefits, especially for parallelized execution.

This merges the role into matrix-synapse while keeping companion logic organized under dedicated reverse_proxy_companion task/template subdirectories.

Compatibility is preserved:
- matrix_synapse_reverse_proxy_companion_* variable names remain unchanged
- install/setup companion-specific tags remain available

Cross-role/global wiring is now in group_vars (matrix-synapse section), while role defaults provide sensible standalone defaults and self-wiring for Synapse-owned values.