Wires `kebab_parse_code::BUILTIN_BLACKLIST` (6 patterns: node_modules,
target, __pycache__, .venv, venv, env) into `build_overrides()` so the
walker automatically excludes these directories even when the user has
no `.kebabignore`. TDD cycle: 2 failing tests added first, then the
pattern-add loop inserted after the existing kbignore block.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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