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.
Adds precompiled Linux x86_64 binaries for yt-dlp and ffmpeg under bin/.
The processor resolves yt-dlp from bin/ when present, falling back to PATH.
ffmpeg is passed via --ffmpeg-location so yt-dlp uses the bundled binary on o2switch.
BIN_DIR is configurable via env var.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>