D6: Execute staged multi-auth rollout and Q0–Q5 go/no-go review

[hieunguyenminhhnl]

Parent epic: #9

Priority: P0
Workstream: D

Scope

Run internal, staging real-provider, allowlisted cohort, and progressive rollout. Assemble acceptance evidence, migration/rollback artifacts, security review, P0 tests, build checks, and stakeholder sign-off.

Acceptance criteria

• Q0–Q5 are green; all P0 blockers closed; no privacy/secret/data delta; production flag only advances when SLOs and reconciliation remain healthy.
• Relevant npm run lint, npx tsc --noEmit, focused tests, and production build checks pass.

Dependencies

All MVP issues, especially D2–D5.

References

• PRD.md
• docs/auth-foundation-plan.md
• docs/auth-ux-plan.md
• docs/auth-quality-security-plan.md