fix: clear analysis data when starting new download

Co-authored-by: Cursor <cursoragent@cursor.com>

src/lib/stores/videoSession.svelte.ts

@@ -103,6 +103,8 @@ export async function beginDownload() {
   session.downloadStatus = 'downloading';
   session.downloadProgress = 0;
   session.localFilePath = null;
+  session.keyframePositions = [];
+  session.waveformPeaks = [];
 
   try {
     await startDownload(