Add IPTV playlist functionality and enhance streaming endpoints

Implemented a new endpoint for downloading the IPTV playlist, allowing users to access a comprehensive M3U file containing all channels and program guides. Updated the StreamingEndpoints to support token validation for both cookie and query parameters, ensuring secure access for external IPTV players. Enhanced the AirPage component to include a download button for the IPTV playlist, with appropriate user feedback on success or failure. Updated localization strings to reflect new features and instructions for users.

backend/src/TeleWave.Application/Streaming/GetIptvGuide/GetIptvGuideQuery.cs

@@ -0,0 +1,10 @@
+using LiteCqrs;
+
+namespace TeleWave.Application.Streaming.GetIptvGuide;
+
+/// <summary>
+/// Телегид сразу по всем включённым каналам — под XMLTV, который IPTV-плеер тянет одним файлом.
+/// Публичный EPG отдаётся по каналу за раз: там это экран зрителя, здесь — выгрузка целиком.
+/// </summary>
+public sealed record GetIptvGuideQuery(DateTimeOffset FromUtc, DateTimeOffset ToUtc)
+    : IQuery<IReadOnlyList<IptvChannelDto>>;