feat: implement /admin add|remove @username command

- Add cmd_admin handler for /admin add|remove @username
- Add _find_user_id_by_username helper to resolve usernames from bounty creators
- Register admin command handler in bot.py
- Add 'admin' to bot command list
- Addresses issue #51

apps/telegram-bot/bot.py

@@ -8,6 +8,7 @@ from telegram.ext import Application, CommandHandler, MessageHandler, filters
 
 from commands import (
     cmd_add,
+    cmd_admin,
     cmd_bounty,
     cmd_delete,
     cmd_edit,
@@ -45,6 +46,7 @@ def build_app() -> Application:
     app.add_handler(CommandHandler("untrack", cmd_untrack))
     app.add_handler(CommandHandler("show", cmd_show))
     app.add_handler(CommandHandler("timezone", cmd_timezone))
+    app.add_handler(CommandHandler("admin", cmd_admin))
 
     app.add_handler(MessageHandler(filters.COMMAND, cmd_help))
 
@@ -62,6 +64,7 @@ async def post_init(app: Application) -> None:
             ("untrack", "Stop tracking"),
             ("show", "Show bounty details"),
             ("timezone", "Get/set room timezone"),
+            ("admin", "Manage admins"),
             ("help", "Show help"),
         ]
     )