Support replying directly to the trigger comment for main commands (e.g., /review, /improve)

Feature request

It would be highly beneficial if PR-Agent supported an option (e.g., reply_to_trigger_comment = true) that publishes the output of main commands like /review and /improve as a direct reply (thread) to the user's triggering comment, instead of creating a standalone root-level comment.

This behavior is already implemented for the /ask command (via the reply_to_comment_from_comment_id method in git providers) and could be extended to other commands to allow them to reply directly to the command trigger.

Motivation

This issue (lack of supporting mentioned feature) can disrupt the flow of the discussion, especially in active PRs, because the AI's response is visually disconnected from the user's initial triggering comment. Extending the reply functionality to the main commands would greatly improve the conversational experience, context tracking, and thread organization within GitLab, GitHub, and other supported platforms.