[telemetry] Telegram bot: profit alerts + error notifications + daily summary

[obchain]

Context

For a bot running headless on a VPS, push notifications are how you know it's alive. Telegram is free, supports markdown, mobile, web, and desktop clients — and the Bot API is dead-simple HTTP.

Scope

• charon-telemetry/src/alerts.rs with a TelegramNotifier
• Config: bot_token, chat_id (via env vars, not in TOML)
• Events:
  • Profit alert — every successful liquidation (amount + tx hash link)
  • Error notification — panics, RPC disconnects, > N consecutive tx failures
  • Daily summary — once per UTC day: total profit, liquidation count, uptime %
• Rate-limiting (max 20 msgs / minute to avoid Telegram throttling)
• Graceful fallback: if Telegram API is down, log locally and keep running

Acceptance criteria

• Sends a startup message when the bot launches
• Successful liquidation triggers a formatted alert with tx link
• Rate limiter drops/queues excess messages with a WARN log
• Missing TELEGRAM_* env vars disables the notifier without crashing
• Daily summary fires at 00:00 UTC

References

• PRD section 7a (Telemetry & Alerting)
• Telegram Bot API: https://core.telegram.org/bots/api

[obchain]

Deferred. Grafana Cloud free-tier alerting covers the M4 demo surface; Telegram sink can be revisited as a polish item post-launch.