v2.4.0 — Matrix command list as room topic

Added

• Matrix: command list published as the room topic. Element (X) has no bot-command menu UI, so Matrix users had no way to discover commands beyond knowing /help. The matrix transport's register_menu now formats the command list as a one-line topic (Commands: /help /status … | /help for details) and sets it in every joined room on gateway startup, and in rooms joined via invite — commands change only across a restart, so the topic stays current automatically. The update is skipped when the topic already matches (no "changed the topic" notice per restart). Setting a topic needs power level ≥ 50 in the room; where the bot is a plain member the failure is logged and everything else proceeds.