#13430: fix(discord): properly handle bot-sent @everyone mentions

Fixes the issue where bot-sent @everyone mentions were not being properly routed. This ensures that mentions from the bot are handled correctly in the Discord channel. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR adjusts Discord preflight mention detection by changing how `hasAnyMention` is computed when `message.mentionedEveryone` is true, intending to handle bot-sent `@everyone` mentions differently during routing/mention-gating. The change is localized to `src/discord/monitor/message-handler.preflight.ts`, where `hasAnyMention` is passed into `matchesMentionWithExplicit(...)` and later into `resolveMentionGatingWithBypass(...)` to decide whether messages should be treated as “mentioned” (and therefore eligible for handling) in guild channels that require mentions. <h3>Confidence Score: 2/5</h3> - Not safe to merge as-is; change breaks `@everyone` mention detection in common cases. - The only functional change modifies `hasAnyMention` so that `mentionedEveryone` no longer counts unless `mentionedUsers.length > 0`, which will make real `@everyone` pings appear as having no mentions and can cause incorrect mention-gating behavior (dropping messages when mentions are required). - src/discord/monitor/message-handler.preflight.ts <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->