Python: Add Telegram hosting helpers and local samples

[eavanvalkenburg]

Parent: #6265

Build the Telegram protocol conversion seam for app-owned Agent Framework hosting without restoring the deleted channel/host runtime.

Scope

• Add python/packages/hosting-telegram/** with side-effect-free Telegram Bot API update parsing and AF conversion helpers.
• Add final and streaming AF response rendering to Telegram Bot API operations.
• Add python/samples/04-hosting/af-hosting/local_telegram/** with self-contained aiogram polling and FastAPI webhook entry points.
• Keep polling, webhook registration, authentication, commands, media download, delivery, retries, throttling, and state policy in application code.
• Update package metadata, sample indexes, and the helper-first hosting design documentation.

Done when

• Text, captions, supported media, callback data, commands, session isolation, final rendering, and streaming rendering are covered by focused tests.
• Tests use tests/hosting_telegram/ with no tests/__init__.py.
• The local polling and webhook samples use an actual Agent Framework agent and native aiogram/FastAPI constructs.
• Package and sample validation pass.

The Foundry-hosted Telegram + Invocations sample is deferred to the separate Invocations protocol work.

[eavanvalkenburg]

Reopened for the follow-up Telegram helper-first work after the core/responses helper surface in #6891.