#21244: fix(discord): defer own-mode fetch until thread allow checks pass

## Summary - Restore this PR to its original scope: defer Discord reaction own-mode message fetch until allowlist/channel gates pass. - Avoid unnecessary `message.fetch()` when notifications are blocked by channel/thread policy. - Keep behavior unchanged for allowed notifications; only reorder gate evaluation. ## Why In own reaction mode, we should not fetch message author metadata before we know the thread/channel is eligible for notification. This reduces unnecessary API calls and aligns with gate-first logic. ## Files - `src/discord/monitor/listeners.ts` ## Commit - `28769a794bfc2ba8d9a2c2b62da6bfc2b32eaa33`