Add Telegram sticker understanding and replies

[crankshift]

Summary

• Add Telegram sticker visual understanding with static attachments, generated previews, cache validation, and saved sticker pack management.
• Add saved sticker replies for explicit sticker requests and eligible reaction markers, including safe description catalog support.
• Bump package version to 0.6.0 and document sticker support behavior.

Test Plan

• pnpm test
• pnpm run check

Closes #20