fix(audit-tier-2): error-surface hygiene — toastError + CodedError sweep

Two mechanical sweeps closing the audit's HIGH §16 + MED §11 findings:

* 38 client components / 56 toast.error sites converted to
  toastError(err) so the new admin error inspector becomes usable from
  user-reported issues — every failed inline-edit, save, send, archive,
  upload, etc. now carries the request-id + error-code (Copy ID action).
* 26 service files / 62 bare-Error throws converted to CodedError or
  the existing AppError subclasses.  Adds new error codes:
  DOCUMENSO_UPSTREAM_ERROR (502), DOCUMENSO_AUTH_FAILURE (502),
  DOCUMENSO_TIMEOUT (504), OCR_UPSTREAM_ERROR (502),
  IMAP_UPSTREAM_ERROR (502), UMAMI_UPSTREAM_ERROR (502),
  UMAMI_NOT_CONFIGURED (409), and INSERT_RETURNING_EMPTY (500) for
  post-insert returning-empty guards.
* Five vitest assertions updated to match the new user-facing wording
  (client-merge "already been merged", expense/interest "couldn't find
  that …", documenso "signing service didn't respond").

Test status: 1168/1168 vitest, tsc clean.

Refs: docs/audit-comprehensive-2026-05-05.md HIGH §16 (auditor-H Issue 1)
+ MED §11 (auditor-G Issue 1).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/services/portal-auth.service.ts

@@ -8,7 +8,13 @@ import { systemSettings } from '@/lib/db/schema/system';
 import { env } from '@/lib/env';
 import { sendEmail } from '@/lib/email';
 import { activationEmail, resetEmail } from '@/lib/email/templates/portal-auth';
-import { ConflictError, NotFoundError, UnauthorizedError, ValidationError } from '@/lib/errors';
+import {
+  CodedError,
+  ConflictError,
+  NotFoundError,
+  UnauthorizedError,
+  ValidationError,
+} from '@/lib/errors';
 import { logger } from '@/lib/logger';
 import { createPortalToken } from '@/lib/portal/auth';
 import { hashPassword, hashToken, mintToken, verifyPassword } from '@/lib/portal/passwords';
@@ -71,7 +77,9 @@ export async function createPortalUser(args: {
     .returning({ id: portalUsers.id });
 
   if (!user) {
-    throw new Error('Failed to create portal user');
+    throw new CodedError('INSERT_RETURNING_EMPTY', {
+      internalMessage: 'Failed to create portal user',
+    });
   }
 
   await issueActivationToken(user.id, normalizedEmail, args.portId);