Add admin controls for selected user params and user note enrichment

Agent-Logs-Url: https://github.com/kr0sh512/tt-simple/sessions/34c3052e-7b55-4cb8-9fee-0ee1ba315691

Co-authored-by: kr0sh512 <46405586+kr0sh512@users.noreply.github.com>

README.md

@@ -13,9 +13,11 @@ Async Telegram bot for selling and extending Marzban VPN subscriptions.
   - `data_limit_reset_strategy = month`
   - `proxies = {"vless": {"flow": "xtls-rprx-vision"}}`
   - `inbounds = {"vless": ["VLESS TCP REALITY"]}`
+  - `note` containing Telegram first name, last name, and phone (if available)
 - If user has active subscription, a new purchase extends from current expiration.
 - Bot sends **subscription URL** after successful purchase.
 - Admin notifications for every creation/extension.
+- Per-user price multiplier support (`price_multiplier`) that affects invoice stars (final amount is always integer).
 - `/stats` command for admins:
   - payments count
   - stars earned
@@ -23,6 +25,13 @@ Async Telegram bot for selling and extending Marzban VPN subscriptions.
   - marzban users
   - traffic usage/total quota
 
+## Admin user management
+- `/select_user <username|telegram_id>` — select user for further updates and show current values.
+- `/selected_user` — show the currently selected user and current values.
+- `/set_expire <YYYY-MM-DD or ISO datetime>` — set selected user expiration (UTC).
+- `/set_traffic <GB>` — set selected user monthly traffic limit in GB.
+- `/set_multiplier <float>` — set selected user price multiplier.
+
 ## Setup
 ```bash
 python -m venv .venv