Add mention_only support for the Mattermost channel, matching the existing
Discord implementation. When enabled, the bot only processes messages that
contain an @-mention of the bot username, reducing noise in busy channels.
- Add mention_only field to MattermostConfig schema (Option<bool>, default false)
- Rename get_bot_user_id() to get_bot_identity() returning (user_id, username)
- Add contains_bot_mention_mm() with case-insensitive word-boundary matching
and metadata.mentions array support
- Add normalize_mattermost_content() to strip @-mentions from processed text
- Wire mention_only through channel and cron factory constructors
- Add 23 new tests covering mention detection, stripping, case-insensitivity,
word boundaries, metadata mentions, empty-after-strip, and disabled passthrough
Add two Mattermost channel enhancements:
1. thread_replies config option (default: false)
- When false, replies go to the channel root instead of threading.
- When true, replies thread on the original post.
- Existing thread replies always stay in-thread regardless of setting.
2. Typing indicator (start_typing/stop_typing)
- Implements the Channel trait's typing methods for Mattermost.
- Fires POST /api/v4/users/me/typing every 4s in a background task.
- Supports parent_id for threaded typing indicators.
- Aborts cleanly on stop_typing via JoinHandle.
Updated all MattermostChannel::new call sites (start_channels, scheduler)
and added 9 unit tests covering thread routing and edge cases.
