Fixes#2514. The parser treated any non-flag token after a flag as its value,
so `$P generate --toc essay.md` ate essay.md as --toc's value and failed with
"missing input" — the skill's own documented usage only worked when two
boolean flags happened to be adjacent. BOOLEAN_FLAGS enumerates the no-value
flags; value flags (--watermark, --to, --title, ...) are unchanged. main()
now runs behind import.meta.main so tests import the parser directly.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
