feat(invoicing): opt-in invoice email from the company's own sending domain (#1802)

* feat(invoicing): opt-in invoice email from the company's own sending domain

Companies holding the custom_sender_domain capability grant can register
their own domain (Resend sending-only profile), publish DKIM/SPF, and once
verified every invoice email (send, reminders, recurring, payment
confirmation, MCP/v1 sends) leaves as "<name> <faktura@their-domain>"
instead of the platform sender. Reply-To is unchanged.

- New table company_sending_domains (RLS: members read, owner/admin write;
  audit trigger), types, archive-export classification.
- New capability key custom_sender_domain: manually granted per company,
  deliberately outside PAID_CAPABILITIES (never trial-seeded, never written
  by the Stripe sync). Without the grant the settings section is hidden and
  nothing changes.
- Email extension: sending-domain routes (GET/POST/PATCH/DELETE, verify),
  Resend domain lifecycle without orphan adoption, domain.updated handling
  on the delivery webhook, explicit From support in the Resend adapter.
- Core resolveInvoiceSender(): verified + enabled + entitled, else the
  platform sender; never throws.
- Settings -> Invoicing: "Avsändare vid fakturautskick" section (sv/en).
- Unit tests for the resolver, domain helpers, routes, From header; pg-real
  test for RLS and constraints.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(invoicing): harden sending-domain writes, sender fallback, review findings

Skeptic refutations:
- Tenant JWTs could insert/update company_sending_domains with status =
  'verified' and an arbitrary domain through PostgREST (RLS only checked
  membership), then send invoice mail as that domain. New migration
  20260822130000 adds a BEFORE trigger: tenants may only open a pending
  claim and edit sender_local_part/sender_name/enabled; domain and
  verification state are service-role only. claim/verify helpers now take
  a service-role writer for those columns; the route's RLS client still
  does the insert.
- A company domain Resend later rejects made every invoice send fail: the
  Resend adapter retries once as the platform sender when an explicit
  company From is rejected (nothing was sent, so no double send).

Review findings:
- domain.updated webhook: discriminated outcome; DB errors answer 500 so
  Svix retries, unknown domains are acknowledged.
- Display names are RFC 5322-quoted only when they carry specials.
- Sender local part is a strict dot-atom (no trailing/consecutive dots),
  in code and in the CHECK constraint; resend_domain_id index is UNIQUE.
- IME composition guard on the claim input; event bus reset in tests;
  settings section skips its request for non-admins.

Deferred (needs a product call): persisting the effective From address in
the invoice delivery log touches the hardened evidence triggers; recorded
in DECISIONS.md.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(invoicing): bind sending-domain verification to the claimed domain; fix pg test

Skeptic re-check found a TOCTOU: during the claim's Resend round-trip a
tenant could delete and re-insert its pending row under the same id with a
reserved domain, and the service-role writer updated by id alone. Now:
- the claim's verification-state write filters on (id, company_id, domain,
  resend_domain_id IS NULL) and rolls back on zero rows;
- verify and the domain.updated webhook compare Resend's domain name with
  the row before writing verified;
- resolveInvoiceSender refuses reserved platform domains and non-hostnames
  at send time (reserved-domain logic moved to lib/email/domain-name.ts and
  shared with the claim validator).

pg-real: the case-insensitive uniqueness assertion now expects the
domain_shape CHECK (lowercase enforced) for an uppercase variant and the
unique index for a same-case duplicate.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

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

types/index.ts

@@ -2964,6 +2964,31 @@ export interface CompanyInboundDomain {
   updated_at: string
 }
 
+export type CompanySendingDomainStatus = 'pending' | 'verified' | 'failed'
+
+// A DNS record the user must publish to verify their custom sending domain
+// (verbatim from the Resend domains API; same shape as the inbound records).
+export type SendingDomainDnsRecord = InboundDomainDnsRecord
+
+// Opt-in per-company sender identity for invoice email. Only a row with
+// status = 'verified' AND enabled = true changes the From header; everything
+// else falls back to the platform sender.
+export interface CompanySendingDomain {
+  id: string
+  company_id: string
+  domain: string
+  status: CompanySendingDomainStatus
+  sender_local_part: string
+  sender_name: string | null
+  enabled: boolean
+  resend_domain_id: string | null
+  dns_records: SendingDomainDnsRecord[] | null
+  verified_at: string | null
+  last_checked_at: string | null
+  created_at: string
+  updated_at: string
+}
+
 export interface InvoiceInboxItem {
   id: string
   user_id: string