The role shipped its own copy of the bridge's Dockerfile and templated it
over the cloned source before building. That copy had already drifted from
upstream (e.g. missing libheif-plugin-libde265) and required separate
maintenance (Renovate bumping the base image here instead of upstream).

Build from the cloned repo's own Dockerfile instead, matching every other
self-build role (e.g. matrix-bridge-steam). The Dockerfile now tracks the
pinned bridge version automatically.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>