Discord bot unresponsive when container sleeps

When using `SANDBOX_SLEEP_AFTER` to reduce costs, the Discord bot becomes completely unresponsive:

- Bot shows offline (Gateway WebSocket disconnects when container sleeps)
- Slash commands fail with "The application did not respond"
- Nothing wakes the container - commands can't be delivered to an offline bot

Currently the only workaround is `SANDBOX_SLEEP_AFTER=never`, which defeats the cost-saving purpose.