Harden root doc contract checks against whitespace and EOL variance

[travisjneuman]

Motivation

• The root-doc validator was brittle and could fail CI due to minor formatting differences (leading blank lines, CRLF endings, or incidental whitespace), so it was hardened to avoid false negatives while keeping the contract strict.

Description

• Added a normalize_line helper and made the home-line detection read the second non-empty line, and updated Next/source heading regexes and next-link extraction to tolerate CRLF and surrounding whitespace so the validator is robust across environments.

Testing

• Ran ./tools/check_root_doc_contract.sh, bash -n tools/check_root_doc_contract.sh, and the full suite via ./tools/run_all_curriculum_checks.sh, and all checks passed including markdown link checks, root/level/project contract checks, portable path checks, project Python comment checks, and smoke runs (core smoke 11/11 and elite smoke 3/3).

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Codex Task