v1.3.0 moved the container's runtime paths to a unified MMRELAY_HOME=/data
model (credentials, database, logs, E2EE store, plugins all live under /data).
Legacy /app paths still work until v1.4.

Adapted the role to the new model: drop the three `/app/*` bind mounts and
the `_logs_path` variable, mount `_config_path` read-only at `/config` and
`_data_path` read-write at `/data`, and invoke the container as
`mmrelay --config /config/config.yaml` so the Ansible-managed config stays
separate from runtime data. Also drop the hardcoded `/app/data/...` database
and e2ee store_path overrides from the default config; MMRELAY_HOME defaults
place them under `_data_path/database/` and `_data_path/matrix/store/` on the
host.

* Add Matrix <-> Meshtastic bridge (meshtastic-matrix-relay)

Vendors the meshtastic-matrix-relay (mmrelay) role into roles/custom/
following the conventions used by other bridge roles.

Co-authored-by: luschmar <90399580+luschmar@users.noreply.github.com>

* Add docs and CHANGELOG entry for Matrix <-> Meshtastic bridge

Co-authored-by: luschmar <90399580+luschmar@users.noreply.github.com>

---------

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