Native Telegram Integration #97

Summary

Integrate Telegram bot directly into opencode-manager so it starts automatically when TELEGRAM_BOT_TOKEN is configured.

Background

Currently, Telegram integration requires running external owpenbot (npm package owpenwork) separately.
The requirements.md states: 'When TELEGRAM_BOT_TOKEN is provided, Telegram MUST work'.

Proposed Solution

1. Add native Telegram service using grammy library
2. Auto-start when TELEGRAM_BOT_TOKEN env var is set
3. Add database tables for sessions and allowlist
4. Add Settings UI for Telegram configuration
5. Add API routes for Telegram management

Acceptance Criteria

• When TELEGRAM_BOT_TOKEN is set, Telegram bot starts automatically
• Bot responds to messages via OpenCode
• Session persistence per chat ID
• Optional allowlist for access control
• Settings UI to configure Telegram
• Health endpoint shows Telegram status
• Integration tests verify functionality

Technical Design

Based on owpenbot implementation:

• Use grammy for Telegram API
• Store sessions in SQLite
• Connect to OpenCode via SDK
• Chunk long messages (4096 char limit)