Approve pinned browser SCRAM-SHA-512 after independent verification

Changes: Accept the bounded SHA-512 experiment and ADR, record independent security findings and review handoff, and retain all browser-runtime, WSS, parent-integration and production limitations.
Validation: Fresh-cache npm ci and browser build pass; 87 focused tests and 10 additional signature, verifier-flag and malformed-first checks pass. Newly installed hashed Scramp oracle verifies all three fixed exchanges. Dependency checks confirm 49 locked entries, 25 installed pins/notices and 340 unchanged Stanza files with matching artifact hashes. Canonical RFC digests and installed oracle notices agree; make check passes 72 tooling tests. Actual browser, WSS/live interoperability and release readiness remain untested.
