Mirror the Discord reaction pattern for Telegram:
- 👀 (eyes) when message processing begins
- ✅ (check) on successful completion
- ❌ (cross) on failure
Controlled via TELEGRAM_REACTIONS env var or telegram.reactions
in config.yaml (enabled by default, like Discord).
Uses python-telegram-bot's Bot.set_message_reaction() API.
Failures are caught and logged at debug level so they never
break message processing.
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