Approve S00-021: independently verified browser OMEMO blocker

Changes:
- Wrote state/evidence/S00-021-review.md recording independent re-checks of the
  executor's remediation for S00-004's interruption ("Agent timed out before
  escalation").
- Reproduced both committed probes unchanged: smoke.mjs exit 0 (SMOKE_PASS,
  631-byte session record byte-for-byte reload) and wasm-unsupported.mjs exit 2
  (wasmFiles 0, native-only prebuilds), matching executor evidence exactly.
- Independently re-queried npm registry: @signalapp/libsignal (browser WASM) E404;
  @signalapp/libsignal-client 0.105.0 (native, AGPL-3.0) exists; confirms the
  browser/worker/WASM + OMEMO2 wire-layer blocker is genuine.
- Audited scope via git: commit 30f7f22 touches only the in-scope ADR
  docs/decisions/0003-crypto-library.md plus workflow metadata; experiments/**
  unchanged; working tree clean. No requirement bypass: S00-004 remains blocked,
  ADR 0003 records the honest blocker and forbids done on persistence+Ratchet alone.

Validation:
- make check: 72 tooling tests OK.
- Both probes reproduced, exit codes and output match evidence.
- Acceptance met: interruption repro row exists for next executor; original not
  declared done via bypass.

Task: S00-021
Reviewer agent: auto-security-5d2ae592b569
Role: security
Action: approve