feat(telegram): add message reactions on processing start/complete

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.

gateway/config.py

@@ -582,6 +582,8 @@ def load_gateway_config() -> GatewayConfig:
                     if isinstance(frc, list):
                         frc = ",".join(str(v) for v in frc)
                     os.environ["TELEGRAM_FREE_RESPONSE_CHATS"] = str(frc)
+                if "reactions" in telegram_cfg and not os.getenv("TELEGRAM_REACTIONS"):
+                    os.environ["TELEGRAM_REACTIONS"] = str(telegram_cfg["reactions"]).lower()
 
             whatsapp_cfg = yaml_cfg.get("whatsapp", {})
             if isinstance(whatsapp_cfg, dict):