Fix recording ENOENT: try absolute ffmpeg paths before bare 'ffmpeg'

ffmpegPath() short-circuited on the bare 'ffmpeg' candidate, so the absolute
Homebrew/system paths were never checked. From a terminal PATH covers it, but
the packaged app launched from Finder has a minimal PATH: stopping a
recording failed with 'spawn ffmpeg ENOENT'. Absolute candidates now win;
bare 'ffmpeg' is the last resort.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XVMQ2JhsJ77pGKqcvvFHqc

package.json

@@ -1,6 +1,6 @@
 {
   "name": "dj-visualizer",
-  "version": "1.8.0",
+  "version": "1.8.1",
   "description": "Audio-reactive fractal & abstract visualizer for external display (Mac)",
   "main": "main.js",
   "author": {