[Ecosystem > TMA] Expand TMA overview and add apps communication page

[coalus]

The current TMA section has short overview with just a video and three links.

This should be added:

• Expanded overview: what TMAs are, why they exist, required tech stack, supported clients table
• New "Apps communication" page: how Mini Apps exchange data with Telegram (transport per platform, calling methods, etc)

Follow-up: Next PRs will cover launch parameters & auth, UI components, dev workflow, and SDK overview.