Add deterministic flavour-text inventory

[kim-em]

Adds the objective inventory tooling needed to make the lifecycle overhaul’s human-only flavour-text audit finite and reproducible.

The tool:

• reuses the catalog validator and rejects unexpected manifest-directory entries;
• records exact UTF-8 byte counts and SHA-256 digests for notes, citations, and informal solutions without generating or judging prose;
• writes distinct JSON/Markdown outputs fail-closed and without overwriting; and
• explicitly leaves every entry pending human provenance and quality review.

Current exact-main inventory: 309 problems; 220 have all three fields, 248 notes, 298 sources, and 228 informal solutions.

Local validation: 37 Python tests, real 309-manifest generation, catalog validation, action-pin audit, Ruff E4/E7/E9/F/I, and diff checks. Independent review was clean at script SHA-256 6713e09dd54035b24a436c264f4887510c534a927e68093d035f5c221b03912e.