feat(documents): universal upload-with-fields UI wiring (B3 #11)

Backend foundations were already in place ('generic' CustomDocumentType,
storage-path routing). This wires the UI surface across Documents Hub +
entity file tabs.

- UploadForSigningDialog: interestId now string | null; new entity?,
  folderId?, onCreated? props. Generic path POSTs to new endpoint
  /api/v1/upload-for-signing; interest-scoped paths unchanged.
- uploadDocumentForSigning service: interestId nullable; skips interest
  lookup, pipeline-stage advance, doc-status flip on the generic path.
  Routes file FK + auto-filed folder via either interest.clientId or the
  caller-supplied entity. Validation enforces the matching invariant
  (generic must be interestId=null, type-specific must carry one).
- New menu item in NewDocumentMenu ("Upload & send for signature") on
  Documents Hub root + folder views.
- Upload & send-for-signature button on ClientFilesTab + CompanyFilesTab,
  gated by documents.send_for_signing.

Existing unit tests for the service still pass (validation paths unchanged).

src/components/clients/client-files-tab.tsx

@@ -2,11 +2,14 @@
 
 import { useState } from 'react';
 import { useQueryClient } from '@tanstack/react-query';
+import { Pen } from 'lucide-react';
 
+import { Button } from '@/components/ui/button';
 import { FileGrid } from '@/components/files/file-grid';
 import { FileUploadZone } from '@/components/files/file-upload-zone';
 import { FilePreviewDialog } from '@/components/files/file-preview-dialog';
 import { PermissionGate } from '@/components/shared/permission-gate';
+import { UploadForSigningDialog } from '@/components/documents/upload-for-signing-dialog';
 import { usePaginatedQuery } from '@/hooks/use-paginated-query';
 import { useRealtimeInvalidation } from '@/hooks/use-realtime-invalidation';
 import { useConfirmation } from '@/hooks/use-confirmation';
@@ -21,6 +24,7 @@ interface ClientFilesTabProps {
 export function ClientFilesTab({ clientId }: ClientFilesTabProps) {
   const queryClient = useQueryClient();
   const [previewFile, setPreviewFile] = useState<FileRow | null>(null);
+  const [uploadForSigningOpen, setUploadForSigningOpen] = useState(false);
   const { confirm, dialog: confirmDialog } = useConfirmation();
 
   const { data, isLoading } = usePaginatedQuery<FileRow>({
@@ -64,12 +68,28 @@ export function ClientFilesTab({ clientId }: ClientFilesTabProps) {
   return (
     <div className="space-y-4">
       <PermissionGate resource="files" action="upload">
-        <FileUploadZone
-          clientId={clientId}
-          onUploadComplete={() => {
-            queryClient.invalidateQueries({ queryKey: ['files', { clientId }] });
-          }}
-        />
+        <div className="space-y-3">
+          <FileUploadZone
+            clientId={clientId}
+            onUploadComplete={() => {
+              queryClient.invalidateQueries({ queryKey: ['files', { clientId }] });
+            }}
+          />
+          <PermissionGate resource="documents" action="send_for_signing">
+            <div className="flex items-center justify-end">
+              <Button
+                type="button"
+                variant="outline"
+                size="sm"
+                onClick={() => setUploadForSigningOpen(true)}
+                className="gap-2"
+              >
+                <Pen className="h-4 w-4" aria-hidden />
+                Upload &amp; send for signature
+              </Button>
+            </div>
+          </PermissionGate>
+        </div>
       </PermissionGate>
 
       <FileGrid
@@ -88,6 +108,17 @@ export function ClientFilesTab({ clientId }: ClientFilesTabProps) {
         fileName={previewFile?.filename}
         mimeType={previewFile?.mimeType ?? undefined}
       />
+
+      {uploadForSigningOpen && (
+        <UploadForSigningDialog
+          open={uploadForSigningOpen}
+          onOpenChange={setUploadForSigningOpen}
+          interestId={null}
+          documentType="generic"
+          entity={{ type: 'client', id: clientId }}
+        />
+      )}
+
       {confirmDialog}
     </div>
   );