fix: remove dead CalculateByteOffset C# shim; guard AudioPlayer.calculateByteOffset on parsed format

DeepDrftPublic.Client/Services/AudioInteropService.cs

@@ -128,18 +128,6 @@ public class AudioInteropService : IAsyncDisposable
         }
     }
 
-    public async Task<long> CalculateByteOffset(string playerId, double positionSeconds)
-    {
-        try
-        {
-            return (long)await _jsRuntime.InvokeAsync<double>("DeepDrftAudio.calculateByteOffset", playerId, positionSeconds);
-        }
-        catch
-        {
-            return 0;
-        }
-    }
-
     public async Task<AudioOperationResult> ReinitializeFromOffset(string playerId, long totalStreamLength, double seekPosition)
     {
         return await InvokeJsAsync<AudioOperationResult>("DeepDrftAudio.reinitializeFromOffset", playerId, totalStreamLength, seekPosition);

DeepDrftPublic/Interop/audio/AudioPlayer.ts

@@ -367,6 +367,7 @@ export class AudioPlayer {
      * Calculate byte offset for a time position (for C# layer)
      */
     calculateByteOffset(positionSeconds: number): number {
+        if (!this.streamDecoder.getFormatInfo()) return 0;
         return this.streamDecoder.calculateByteOffset(positionSeconds);
     }