Subcommand name.
One-line description for mediaforge help.
Usage line.
flag -> description shown in help.
A description beginning with = marks a flag that requires a value; every
other flag is boolean and never consumes the following argument. That
declaration is authoritative — buildFlagSpec reads it and the parser acts
on it, so analyze --json input.mp3 parses input.mp3 as a positional.
Positional argument names, in order, for help text.
Run the command. Commands that only print or validate synchronously return
void; everything that shells out to ffmpeg returns a promise.