classify_error now catches 'unexpected token', 'unexpected char',
'expected ident/punct/keyword' as SyntaxError variants.
classify_negative_result maps parser errors to SyntaxError for negative:parse
tests that expect a SyntaxError. Also maps 'undefined symbol' to
ReferenceError for negative:runtime tests. This reclassifies ~39+36 tests
per wide run from 'fail' to 'pass (negative)'.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>