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/admin/brochures-admin-panel.tsx

@@ -29,6 +29,7 @@ import { Label } from '@/components/ui/label';
 import { Textarea } from '@/components/ui/textarea';
 import { Switch } from '@/components/ui/switch';
 import { apiFetch } from '@/lib/api/client';
+import { toastError } from '@/lib/api/toast-error';
 
 interface BrochureRow {
   id: string;
@@ -123,8 +124,7 @@ function BrochureCard({ brochure, onChange }: { brochure: BrochureRow; onChange:
       toast.success('Default brochure updated');
       onChange();
     },
-    onError: (e) =>
-      toast.error(e instanceof Error ? e.message : 'Could not update default brochure'),
+    onError: (e) => toastError(e),
   });
 
   const archiveMutation = useMutation({
@@ -133,7 +133,7 @@ function BrochureCard({ brochure, onChange }: { brochure: BrochureRow; onChange:
       toast.success('Brochure archived');
       onChange();
     },
-    onError: (e) => toast.error(e instanceof Error ? e.message : 'Archive failed'),
+    onError: (e) => toastError(e),
   });
 
   async function handleUpload(file: File) {
@@ -168,7 +168,7 @@ function BrochureCard({ brochure, onChange }: { brochure: BrochureRow; onChange:
       toast.success('New version uploaded');
       onChange();
     } catch (err) {
-      toast.error(err instanceof Error ? err.message : 'Upload failed');
+      toastError(err);
     } finally {
       setUploading(false);
     }
@@ -287,7 +287,7 @@ function CreateBrochureDialog({
       onCreated();
       onOpenChange(false);
     },
-    onError: (e) => toast.error(e instanceof Error ? e.message : 'Could not create brochure'),
+    onError: (e) => toastError(e),
   });
 
   return (