fix: invert reversed storage guard condition in MP4 finalization

The ternary in GetLowStoragePauseMessageAsync had its branches swapped:
when storage was healthy it returned the pause error, and when storage
was critically low it returned null (allowing finalization to proceed).
This caused MP4 finalization to always pause with a misleading 'storage
is Red' warning even when storage protection was disabled.

src/LiveRecorder.Infrastructure/Services/FfmpegService.Utils.cs

@@ -50,8 +50,8 @@ public sealed partial class FfmpegService
             var sourceSizeBytes = new FileInfo(sourcePath).Length;
             var storageCheck = _storageGuardService.CheckCanStartOrResume(settings, sourceSizeBytes);
             return storageCheck.ShouldPauseActive
-                ? null
-                : $"{LowStoragePauseErrorPrefix} {storageCheck.Message}";
+                ? $"{LowStoragePauseErrorPrefix} {storageCheck.Message}"
+                : null;
         }
 
         var lowStoragePauseMessage = await GetLowStoragePauseMessageAsync();