feat: add Linux ffprobe and Windows ffmpeg/ffprobe binaries to bin/

yt-dlp needs ffprobe alongside ffmpeg for postprocessing; only ffmpeg was
bundled for the Linux/o2switch prod deploy. Also add Windows builds so
local dev on Windows has a working ffmpeg/ffprobe pair, and gitignore
.env.prod/.env.local so real deployment credentials never get committed.

.gitignore

@@ -1,6 +1,8 @@
 node_modules/
 .next/
 .env
+.env.prod
+.env.local
 *.log
 storage/
 worker/worker.pid