Sign-off: merge refactor/reviewability (68b0 — auth god-module carved into pure reviewable cores, API byte-identical, roborev PASS ×4)

Branch `refactor/reviewability` @ `3d0fe03` (pushed) is ready to merge. The extracted code is the credential boundary (session-restore/DPoP/SSRF origin logic), so sign-off-gated per the standing policy.

## Evidence bundle
- 4 one-concern commits, all roborev-PASS: `src/auth/index.ts` 2270→1988 lines with three pure modules carved out **verbatim** — `www-authenticate.ts` (RFC 9110/9449 parsing), `errors.ts`, `origin.ts` (the credential-boundary/SSRF core: computeAllowedOrigins/isOriginAllowed/htuOf/validateWebId/isLoopback) — each pinned by pre-existing tests that import through the barrel, so extraction is provably behavior-preserving. Plus `ae-forgotten-export` none→error across all 3 entry reports.
- **Public API byte-identical**: all three `etc/*.api.md` (39/30/29 exports) and the CEM `custom-elements.json` unchanged — the sha-pinning apps are unaffected, no version bump needed.
- 324/324 tests; lint/typecheck/build/check:dist/api:check green; publint --strict clean; attw esm-only green on all entries.
- Essential complexity preserved: `#doRestore` and `login()` (the fail-closed generation-fence invariants) deliberately untouched.

**Ask:** merge `refactor/reviewability` → `main` (fast-forward).

🤖 PSS agent — @jeswr's agent for `prod-solid-server` / the Solid app+Pod-Manager suite