Remove the shared passphrase gate

[pataniaeli]

Ticket: VAULTZ-V02 · Epic: SGAuth integration — VaultZ · Phase: Phase 2 — Admin, Primary Admin, positions, UI, SDK, VaultZ
Priority: High · Estimate: 2 points · Labels: epic:sgauth-integration, phase:2, sgauth, backend

Depends on:

• Install @sgaoperations/sgauth and protect all routes with the SGAuth proxy #747 — VAULTZ-V01 Install @sgaoperations/sgauth and protect all routes with the SGAuth proxy

Delete lib/access-gate.ts, lib/actions/access.ts, the passphrase page, and the VAULTZ_ACCESS_CODE/VAULTZ_ACCESS_SECRET env vars after the cutover (keep behind a SGAUTH_ENABLED flag for one release so rollback is a flag flip, then delete).

Acceptance criteria

• No references to the passphrase remain after the flag is removed; the vaultz_access cookie is no longer set.

_{Generated from the SGAuth design (docs/sgauth-design in SGAOperations/auth). SGAuth is built on Neon and does not use Supabase.}