feat(white-label): invite-only signup for brand domains (#1995)

* feat(white-label): invite-only signup for brand domains

A brand domain belongs to the partner's people (founder decision
2026-08-27): only allowlisted or invited users may create an account on
an invite-only brand domain; everyone else is shown an interstitial that
sends them to the canonical Accounted signup.

- brands.signup_mode ('open' default / 'invite_only') +
  brand_signup_allowlist (lowercase emails, team-scoped RLS, owner/admin
  writes) + create_company_for_brand_signup RPC, with pg-real coverage
- server-side gate (lib/auth/brand-signup-gate.ts) enforced on every
  signup path: email signup moved to POST /api/auth/signup (the browser
  used to call GoTrue directly, so a client-side check would be
  bypassable), BankID gated in /bankid/complete, Google covered by the
  dashboard layout's brand-domain bounce
- company invites bypass the allowlist: the invite is the authorization
- register page interstitial on gated brands (no email in the outbound
  URL), sv+en strings
- dashboard layout bounces non-belonging sessions off gated brand hosts
  to the canonical domain (navigation rule like WL-01, not a security
  boundary)
- allowlisted signups' onboarding-created companies attach to the
  brand's byra team via the new RPC, so WL-01 homes them on the brand
  domain; the allowlist entry recorded by an owner/admin stands in for
  the WL-15 admin gate
- byra cockpit page /clients/access + /api/clients/signup-access to
  manage the mode and the allowlist

All existing brands default to 'open': behavior is byte-identical until
a brand is flipped to invite_only.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ByL5dQXG8gGLtNBPj8g2C4

* fix(white-label): rollback brand-signup company with the service client

Skeptic (correctness) found that a brand-signup company created under the
service role rolled back with the cookie-session client: `companies` has
RLS and no FOR DELETE policy, so the delete was a silent 0-row no-op,
stranding a member-less ghost company on the partner's byra team. Pass an
optional rollbackClient to createCompanyCore and hand it the service
client on that path; user_preferences.active_company_id then clears itself
via its ON DELETE SET NULL FK once the company row is actually deleted.

Also map a validateBody 400 (flat envelope, no code) on the register page
to the specific email-invalid field message instead of the generic one,
since the client already pre-gates password strength.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ByL5dQXG8gGLtNBPj8g2C4

* fix(white-label): fail-safe brand lookup, pg-test seed, anonymize fixtures

Second resolve-pr cycle: skeptic + CodeRabbit findings and a green-up.

- Fail safe on a brands-table error (CodeRabbit CWE-285): the gate treated a
  failed resolveBrandByHost as an unbranded host, opening invite-only signup
  during a transient DB blip. resolveBrandResultByHost now distinguishes
  "no brand" from "lookup failed"; the gate returns lookupFailed and the
  email + BankID routes answer 503 (retry), never creating an account.
- pg-real: the RLS delete test seeded its row inside withUserContext, which
  always rolls back, so the owner DELETE saw zero rows. Seed on the superuser
  pool instead.
- Anonymize every test/fixture brand to the repo's existing synthetic
  placeholder (Siffra / app.siffra.se): no real partner names in code.
- SignupAccessManager: functional setData updates so a concurrent mode
  toggle and an add/remove do not clobber each other's snapshot (CodeRabbit).
- Route a transient-error message through i18n instead of the raw envelope
  (raw-user-error guard); new register.error_temporary sv+en.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ByL5dQXG8gGLtNBPj8g2C4

* test(white-label): anonymize new signup-gate fixtures; log oracle residual

Rename the placeholder brand in the four new brand-signup test files to a
clearly-fake, partner-unrelated name (Testbrand / app.testbrand.example);
the previous placeholder echoed a real partner. Scoped to files this PR
creates; the repo-wide legacy placeholder is left for a separate cleanup.

Also record in DECISIONS.md that the feature ships accepting the
low-severity allowlist-enumeration residual (captcha-free 403 vs 200 on
the signup endpoint), with rate-limiting as the follow-up option.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ByL5dQXG8gGLtNBPj8g2C4

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

lib/api/schemas.ts

@@ -3839,3 +3839,21 @@ export const FiscalYearResetSchema = z.object({
 export const NoticeDismissSchema = z.object({
   notice_id: z.string().min(1).max(200),
 })
+
+/**
+ * Brand signup access (invite-only white-label domains, 2026-08-27).
+ * Emails are lowercased here so they match the CHECK-enforced lowercase
+ * storage in brand_signup_allowlist.
+ */
+export const BrandSignupModeSchema = z.object({
+  signup_mode: z.enum(['open', 'invite_only']),
+})
+
+export const BrandAllowlistAddSchema = z.object({
+  email: z.string().trim().toLowerCase().max(320).pipe(z.string().email()),
+  note: z.string().trim().max(200).optional(),
+})
+
+export const BrandAllowlistRemoveSchema = z.object({
+  id: z.string().uuid(),
+})