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/M3UParser.cs

@@ -221,6 +221,7 @@ namespace TV_Player
         {
             try
             {
+
                 using var client = new HttpClient();
                 using var request = new HttpRequestMessage();
                 client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/text"));
@@ -240,6 +241,11 @@ namespace TV_Player
                 System.Diagnostics.Debug.WriteLine($"Invalid URL: {url} - {ex.Message}");
                 throw;
             }
+            catch (Exception ex)
+            {
+                System.Diagnostics.Debug.WriteLine($"Error reading file from {url}: {ex.Message}");
+                throw;
+            }
         }
 
         public static async Task<(List<M3UInfo> programList, string programGuide)> DownloadM3UFromWebAsync(string url)