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/documents.service.ts

@@ -18,7 +18,7 @@ import { userProfiles, userPortRoles } from '@/lib/db/schema/users';
 import { buildListQuery } from '@/lib/db/query-builder';
 import { createAuditLog, type AuditMeta } from '@/lib/audit';
 import { diffEntity } from '@/lib/entity-diff';
-import { NotFoundError, ValidationError, ConflictError } from '@/lib/errors';
+import { CodedError, NotFoundError, ValidationError, ConflictError } from '@/lib/errors';
 import { emitToRoom } from '@/lib/socket/server';
 import { buildStoragePath } from '@/lib/minio';
 import { getStorageBackend } from '@/lib/storage';
@@ -1412,7 +1412,10 @@ export async function createFromWizard(
     })
     .returning();
 
-  if (!doc) throw new Error('Failed to insert document');
+  if (!doc)
+    throw new CodedError('INSERT_RETURNING_EMPTY', {
+      internalMessage: 'Failed to insert document',
+    });
 
   if (data.watchers.length > 0) {
     await assertWatchersInPort(portId, data.watchers);
@@ -1498,7 +1501,10 @@ export async function createFromUpload(
       createdBy: meta.userId,
     })
     .returning();
-  if (!doc) throw new Error('Failed to insert document');
+  if (!doc)
+    throw new CodedError('INSERT_RETURNING_EMPTY', {
+      internalMessage: 'Failed to insert document',
+    });
 
   await db.insert(documentSigners).values(
     data.signers.map((s) => ({