fusion-lint-requires-exact-section-header-format

The fusion-invariants-lint.py script enforces EXACT ### N. Title header format for the 14-invariant sections in each SKILL.md. Any deviation (missing number, wrong markdown depth, extra spaces) causes a lint failure. Duplicate numbering — where sections 9 and 10 appear twice in the same file — passes write silently but creates an ambiguity debt that must be resolved via progressive disclosure.