fix(test): update media-understanding tests for whisper skip empty audio

Increase test audio file sizes to meet MIN_AUDIO_FILE_BYTES (1024) threshold
introduced by the skip-empty-audio feature. Fix localPathRoots in skip-tiny-audio
tests so temp files pass path validation. Remove undefined loadApply() call
in apply.test.ts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/media-understanding/runner.test-utils.ts

@@ -49,7 +49,7 @@ export async function withAudioFixture(
       filePrefix,
       extension: "wav",
       mediaType: "audio/wav",
-      fileContents: Buffer.from("RIFF"),
+      fileContents: Buffer.alloc(2048, 0x52),
     },
     run,
   );