0.9.0dev6

[rlippmann]

What changed

• Removed the redundant is_canonical_directive() grammar API helper.
• Clarified grammar API boundaries:
  • use validate_directive() for canonical directive classification;
  • use decompose_directive() when operands are required;
  • use match_canonical_directive_start() only for shallow syntax detection.
• Documented that directive text fields preserve accepted input text and are not canonical rendered output.
• Bumped the development release version.

Why

• Reduce redundant public API surface.
• Keep Python and TypeScript grammar contracts smaller and easier to maintain.
• Make parsing, validation, and rendering responsibilities explicit.

Checklist

• pre-commit run (uv run pre-commit run --all-files)
• tests pass (uv run pytest)