feat: react to incoming user messages with a random emoji ack

[danieliyahu1]

Adds a middleware that reacts to every incoming user message with a random emoji from a curated pool of 26 Telegram-supported reaction emojis.

• Fire-and-forget — never blocks message processing
• Registered after auth, before interaction guard — user sees ack even when busy
• Existing rate-limit retry wrapper handles Telegram rate limits gracefully
• Includes unit tests for emoji selection

[grinev]

@danieliyahu1 thanks for the PR. Now bot shows typing indicator when user message is handled. I don't undestand the purpose of this change, what problem this change will solve?

[danieliyahu1]

@grinev it's much nicer as a user to get a reaction which is more visible to human eye to know the message got to the bot.
The typing is great but less visible, the typing is better for long time response.
This feature is nice to have, I saw it on other agents and liked it more so I thought it will be great to have it here.