feat(account): self-service login email change with double confirmation (#2017)

* feat(account): self-service login email change with double confirmation

New POST /api/account/email requests the change via the user session so
Supabase's AAL2 guard applies, and the account settings page gets an email
row with pending-confirmation state. Confirmation mails (both addresses)
and the /auth/callback email_change verification already existed; this
wires the missing initiation.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018sbGMZQE5W7KfSVFjK7E4p

* feat(account): map email_exists to a 409 with Swedish copy

Changing to an address that already has an account is refused by GoTrue
(addresses are unique per auth user); surface that as a clear conflict
instead of the generic fallback.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018sbGMZQE5W7KfSVFjK7E4p

* fix(account): trusted redirect origin + profiles.email sync trigger (skeptic findings)

- emailRedirectTo now derives from resolveRequestAppOrigin(): request.url
  can be an internal origin behind a proxy (dead confirmation links on
  self-hosted) and auth links must not follow attacker-chosen hosts;
  registered white-label hosts keep their brand.
- New migration 20260828191950: sync_profile_email trigger mirrors
  auth.users.email changes into profiles.email (member lists, notification
  recipients, AGI/KU contact, invite dedup all read profiles.email), plus a
  backfill for already-diverged rows. pg-real test included.
- Save button disabled while the same address awaits confirmation (no
  rate-limit re-fires); GoTrue's 'error sending email change email' now maps
  to the Swedish SMTP guidance.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018sbGMZQE5W7KfSVFjK7E4p

* fix(account): idempotent repeat request for the pending address

CodeRabbit follow-up: a second POST for the address already awaiting
confirmation now returns the pending state without another GoTrue round
trip (no duplicate confirmation mails, no rate-limit burn). Claims-mapped
sessions lack new_email; GoTrue's send rate limit remains the backstop.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018sbGMZQE5W7KfSVFjK7E4p

---------

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

lib/errors/get-error-message.ts

@@ -160,7 +160,7 @@ const ERROR_PATTERN_MAP: [RegExp, string | null][] = [
   [
     // GoTrue could not send its own mail (admin invite, confirmation,
     // recovery): almost always missing SMTP configuration on self-hosted.
-    /error sending (invite|confirmation|recovery|magic link) email/i,
+    /error sending (invite|confirmation|recovery|magic link|email change) email/i,
     'E-postmeddelandet kunde inte skickas av autentiseringstjänsten. Kontrollera installationens SMTP-inställningar och försök igen.',
   ],
 ]