Remove dead code: utils/deeplink.py is unused

[fengtality]

Summary

utils/deeplink.py contains a decode_deeplink() function for decoding base64url-encoded server credentials from Telegram deep links (t.me/condorbot?start=<payload>).

This function is never imported or called anywhere in the codebase. There is also no corresponding encode_deeplink — nothing generates these links.

Recommendation

Delete utils/deeplink.py. If deep link registration is needed in the future, it can be reimplemented with proper encryption (current implementation uses plain base64 encoding, which is not secure for credentials).

Found during

Code review of PR #36.