prose-pointer-lint-must-check-skills-root-docs-not-just-skill-local

When extending fusion-invariants-lint.py to detect dead prose pointers, the initial implementation resolved docs/X.md relative to each individual skill’s directory, causing 10 false errors on governance docs that live at skills-root-level /root/.claude/skills/docs/. The fix is to check both the skill-local path AND the skills-root-level docs/ path before flagging a reference as dead.