Fail closed on missing node-compat suite inputs

[noise64]

• makes node-compat configuration and report loading fail when the pinned vendored suite is absent, its Node version differs from config.jsonc, or a source required for implicit Node-internals classification is missing
• replaces the silent missing-source fallback that could misclassify Node-internal tests as runnable
• documents the vendored-source dependency in the generator, checked-in report, and node-compat workflow
• adds four CI-enforced regression cases for missing, mismatched, and valid suite inputs
• narrows the report generator helper to the writing test so it cannot race report generation against currentness validation

Node compatibility

• primary CI-enforced: 3180/4387 (72.5%) → 3180/4387 (72.5%)
• full public: 3180/5750 (55.3%) → 3180/5750 (55.3%)
• no compatibility classifications or runnable cases change; this makes the existing inventory fail closed when its required inputs are unavailable