MAS now connects to the playbook-managed Postgres via a UNIX socket by
default (when available), matching the approach already used by Synapse.

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

syn2mas reads Synapse's homeserver.yaml and reuses the database
connection details from there.

When Synapse is configured to reach the integrated Postgres over a UNIX socket,
the temporary syn2mas container was given the config file but not the socket mount,
so migrations could fail even though Synapse itself was configured correctly.

Wire the Synapse socket settings into MAS via playbook vars and mount
the same socket path into the syn2mas container, so migrations work in
socket-based deployments without coupling the MAS role directly to
Synapse role variables.

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

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

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

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/4297

Supersedes https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/4300

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

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

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3108

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/3562