[Feature] Auto-close lab status at 2am daily

Summary

The lab status (open / closed) is currently set entirely through chat commands (bot lab is open, bot lab is closed). There's no automatic behavior — if someone forgets to set it to closed at night, it stays stale.

Problem

• Lab status can remain open long after the lab has closed, giving members incorrect information.
• Someone has to remember to manually update it every night.

Proposed behavior

• Use a scheduled task (cron-style) to automatically set the lab status to closed at 2:00 AM IST daily.
• The bot should send a message to the designated channel when it does so, e.g.:

  🕐 Lab is now closed (auto-updated at 2:00 AM).
  

• The existing manual commands (bot lab is open, bot lab is closed) continue to work as before and override the auto-status until the next scheduled reset.

Implementation notes

• The project already depends on node-cron — use it to schedule the task on bot startup.
• The timezone should be Asia/Kolkata (already set in the Docker environment).
• The cron expression for 2:00 AM IST daily: 0 2 * * *.

Acceptance criteria

• Lab status automatically changes to closed at 2:00 AM IST every day.
• A notification message is posted to the channel when the auto-close happens.
• Manual bot lab is open after 2:00 AM correctly overrides the status until the next night.
• Works correctly across timezone/DST boundaries (IST has no DST, so this is straightforward).