feat(17-03): implement Telegram bot command handlers
- Add telego v1.8.0 dependency for Telegram Bot API
- Create pkg/bot package with Bot struct holding engine, verifier, recon, storage, registry deps
- Implement 8 command handlers: /help, /scan, /verify, /recon, /status, /stats, /providers, /key
- /key enforced private-chat-only for security (never exposes unmasked keys in groups)
- All other commands use masked keys only
- Handler registration via telego's BotHandler with CommandEqual predicates
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