fix(web-test): update ffmpeg download links and clarify prerequisites

Use direct gyan.dev URL instead of generic ffmpeg.org. Rewrite recording.md
prerequisites as clear alternatives (project / global / config).

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

.claude/skills/web-test/scripts/browser.mjs

@@ -2562,7 +2562,7 @@ function resolveFfmpeg(explicit) {
   // 5. Error with instructions
   throw new Error(
     'ffmpeg not found. Install it:\n' +
-    '  - Download from https://ffmpeg.org/download.html\n' +
+    '  - Download from https://www.gyan.dev/ffmpeg/builds/ (essentials build)\n' +
     '  - Add to PATH, or set FFMPEG_PATH env var, or place in tools/ffmpeg/bin/\n' +
     '  - Or pass ffmpegPath option to startRecording()'
   );