v2.5.0 — Matrix image/vision support

Images sent to the bot over Matrix now reach the assistant layer: the transport yields media messages (mxc url, filename, mimetype, caption) and downloads them via the authenticated media endpoint (legacy fallback included); the gateway saves images into the LLM workspace and Claude views them natively with its Read tool — captions included. Non-image files get a notice; size capped at 10 MB, saved copies pruned after 14 days. Encrypted media stays out of scope (no-E2EE design). CI now also syntax-checks transport_matrix.py.

See CHANGELOG.md for details.