Approve storage design after independent transaction checks

Changes: Accept ADR 0004 and record independent S00-005 review, experiment status and handoff; preserve explicit native browser and durability limitations.
Validation: Fresh-cache npm ci and npm run check passed on Node 24.21.0/npm 11.19.0; exact lock pins, HTTPS/SHA512, installed license texts and runtime refusal checks passed. make check passed 72 tooling tests. Scoped diff and whitespace reviewed; native browser quota and process restart were not tested.
