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/components/invoices/invoice-detail.tsx

@@ -25,6 +25,7 @@ import {
 import { Tabs, TabsContent, TabsList, TabsTrigger } from '@/components/ui/tabs';
 import { InvoicePdfPreview } from './invoice-pdf-preview';
 import { apiFetch } from '@/lib/api/client';
+import { toastError } from '@/lib/api/toast-error';
 import { useMobileChrome } from '@/components/layout/mobile/mobile-layout-provider';
 import { recordPaymentSchema, type RecordPaymentInput } from '@/lib/validators/invoices';
 
@@ -99,7 +100,7 @@ export function InvoiceDetail({ invoiceId }: InvoiceDetailProps) {
       queryClient.invalidateQueries({ queryKey: ['invoices', invoiceId] });
       queryClient.invalidateQueries({ queryKey: ['invoices'] });
     },
-    onError: (e) => toast.error(e instanceof Error ? e.message : 'Could not send invoice'),
+    onError: (e) => toastError(e),
   });
 
   const paymentForm = useForm<RecordPaymentInput>({
@@ -118,7 +119,7 @@ export function InvoiceDetail({ invoiceId }: InvoiceDetailProps) {
       queryClient.invalidateQueries({ queryKey: ['invoices', invoiceId] });
       queryClient.invalidateQueries({ queryKey: ['invoices'] });
     },
-    onError: (e) => toast.error(e instanceof Error ? e.message : 'Could not record payment'),
+    onError: (e) => toastError(e),
   });
 
   if (isLoading) {