When a user @mentions an agent in any issue's comment, the system now
enqueues a task for that agent. The agent reads the issue context and
replies to the triggering comment thread.
Changes:
- Add shared util.ParseMentions for mention parsing (used by both
comment handler and notification listeners)
- Add EnqueueTaskForMention to TaskService for explicit agent targeting
- Add on_mention trigger type support in agent trigger config
- Add HasPendingTaskForIssueAndAgent SQL query for per-agent dedup
- Add enqueueMentionedAgentTasks in CreateComment handler
Safety: prevents self-trigger (agent mentioning itself), dedup with
assignee on_comment trigger, terminal issue status check, and per-agent
pending task dedup.
37881adbed