Fix Discord crash/hang when exiting immediately after startup

[gokr]

Summary

When Discord integration is enabled, exiting Niffler immediately after startup can either hang during shutdown or crash in the Discord thread before the bot reaches ready state.

Reproduction

1. Ensure Discord integration is enabled in config/database.
2. Start ./niffler.
3. Immediately run /quit.

Observed behavior

• The process may hang during shutdown.
• In some runs it crashes in the Discord thread with a SIGSEGV from asyncnet/dimscord startup.
• If startup is allowed to settle first, shutdown is much more reliable.

Notes

• Normal shutdown after Discord reaches ready state appears to work.
• The failure window is specifically the startup phase before the Discord bot is fully ready.
• The Action refactor work is not the root cause; it only made the quick-exit smoke test expose the existing startup-window bug more consistently.

Current context

Observed while testing around commit 4f13766.