Support local file paths for M3U playlists; UI tweaks

Added support for loading M3U playlists from both web URLs and local file paths, with logic to resolve relative paths. Improved exception handling in M3UParser. Enabled toggling of window border style in fullscreen mode, with data binding for WindowStyle. Removed IsValidUrl check to allow local file sources in settings. Cleaned up usings and formatting. Removed .NET SDK version from global.json.

TV Player Core/ProgramsData.cs

@@ -1,5 +1,10 @@
-using System.Reactive;
+using System;
+using System.IO;
+using System.Linq;
+using System.Reactive;
 using System.Reactive.Subjects;
+using System.Threading.Tasks;
+using System.Collections.Generic;
 
 namespace TV_Player
 {
@@ -25,7 +30,33 @@ namespace TV_Player
             //string m3uLink = "http://pl.da-tv.vip/a71e77fa/835b3216/tv.m3u";
             try
             {
-                var result = await M3UParser.DownloadM3UFromWebAsync(m3uLink);
+                // if link is a well-formed absolute URI load from web, otherwise treat as a local file path
+                // for relative paths try resolving against the application's base directory
+                var result = (programList: new List<M3UInfo>(), programGuide: string.Empty);
+                if (Uri.IsWellFormedUriString(m3uLink, UriKind.Absolute))
+                {
+                    System.Diagnostics.Debug.WriteLine("[ProgramsData] Detected URL, downloading from web");
+                    result = await M3UParser.DownloadM3UFromWebAsync(m3uLink);
+                }
+                else
+                {
+                    // try as provided path first
+                    var candidate = m3uLink;
+                    if (!Path.IsPathRooted(candidate))
+                    {
+                        candidate = Path.Combine(AppContext.BaseDirectory ?? string.Empty, candidate);
+                    }
+
+                    if (File.Exists(candidate))
+                    {
+                        System.Diagnostics.Debug.WriteLine($"[ProgramsData] Detected local file, loading from disk: {candidate}");
+                        result = await M3UParser.DownloadM3UFromWebAsync(candidate);
+                    }
+                    else
+                    {
+                        throw new FileNotFoundException($"M3U file not found: {m3uLink}");
+                    }
+                }
                 System.Diagnostics.Debug.WriteLine($"[ProgramsData] Downloaded {result.programList.Count} programs");
 
                 programsSubject.OnNext(result.programList);