debug: add logging to _find_user_id_by_username

To see the actual error when user lookup fails.

apps/telegram-bot/commands.py

@@ -775,10 +775,15 @@ async def _find_user_id_by_username(
     ctx: ContextTypes.DEFAULT_TYPE, username: str
 ) -> int | None:
     """Find user_id by username using Telegram API."""
+    import logging
+
+    log = logging.getLogger(__name__)
     try:
         chat = await ctx.bot.get_chat(f"@{username}")
+        log.info(f"Found user {username}: {chat.id}")
         return chat.id
-    except Exception:
+    except Exception as e:
+        log.error(f"Failed to find user @{username}: {e}")
         return None