Patch release: standalone CALL accepts non-reserved keywords such as
`union` as procedure or yield names, nested-fragment syntax errors point
at the offending token, and the crate docs gained a getting-started
walkthrough and scope notes. Bumps the crate and both lockfiles and the
README snippets.

Also ledgers the `top_level_indices` depth-increment mutant, which became
unobservable once the standalone-CALL fallback stopped consulting
top-level UNION tokens.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>