Feature: Require "reply" or "r" prefix when replying

As the title suggests. When users precisely want to reply to an issue. Users will never mind adding words when they need this feature. It also prevents users from misusing and reduces the bot's message sending.

No file, test, or entry point is named in the issue. Start by locating the plugin's handling of issue replies and review how reply intent is detected; done means replies are processed only when the message begins with "reply" or "r", while other messages do not trigger the bot's reply behavior.

Written by the indexing model from the issue text.