Add Telegram bot for group notifications (#60)

[zsheng823]

Summary

This PR implements a Telegram bot for monitoring SoroSave group events, as requested in issue #60.

Features

• ✅ Telegram bot using Grammy framework
• ✅ /subscribe <group_id> - Subscribe to group notifications
• ✅ /unsubscribe <group_id> - Unsubscribe from a group
• ✅ /status - View current subscriptions
• ✅ /help - Show help message
• ✅ NotificationService for sending event notifications
• ✅ Support for:
  • New contributions
  • Payout distributions
  • Round started events

Files Added

• telegram-bot/package.json - Dependencies
• telegram-bot/tsconfig.json - TypeScript config
• telegram-bot/.env.example - Environment template
• telegram-bot/.gitignore - Git ignore file
• telegram-bot/README.md - Documentation
• telegram-bot/src/index.ts - Main bot code

Testing

cd telegram-bot
npm install
cp .env.example .env
# Edit .env and add your bot token
npm run dev

Closes #60