Feature: Add Telegram allowlist access control fields to Desktop GUI

## Problem

The Telegram tab in the Desktop GUI only shows 5 fields: bot_token, base_url, http_proxy, http_proxy_auth, show_typing.

Users cannot set: allow_from, dm_policy, group_policy, access_control_dm, access_control_group, dm_disabled, group_disabled — all required for restrict-who-can-access-the-bot (allowlist/denylist).

These fields work in the backend and are shown for Matrix/imessage, but NOT for Telegram.

## Current Pain

To restrict access, users must manually edit config.json and add ALL of these:

```json
"telegram": {
"dm_policy": "allowlist",
"group_policy": "allowlist",
"access_control_dm": true,
"access_control_group": true,
"allow_from": [YOUR_TELEGRAM_ID]
}