feat(bot): register Telegram command menu on startup

Set /start, /newsession, /listsessions, /exportcalendar and /help
via setMyCommands for both private chats and group chats so users
see the command list when typing '/'.

Also update /help text to list all commands first and then show the
example.

src/GmRelay.Bot/Program.cs

@@ -98,6 +98,7 @@ builder.Services.AddSingleton<DirectSessionNotificationSender>();
 // ── Telegram infrastructure ──────────────────────────────────────────
 builder.Services.AddSingleton<UpdateRouter>();
 builder.Services.AddSingleton<ITelegramUpdateHandler>(sp => sp.GetRequiredService<UpdateRouter>());
+builder.Services.AddHostedService<TelegramCommandsSetupService>();
 builder.Services.AddHostedService<TelegramMiniAppMenuButtonService>();
 builder.Services.AddHostedService<TelegramBotService>();