fix(audit-wave-9): standardize on Sheet for previews; doctrine in CLAUDE.md

Swap the one outlier (client-interests-tab.tsx) from Vaul Drawer to
Sheet side=right so every detail-preview surface uses the same
primitive. Document the doctrine: Sheet for side panels on both desktop
and mobile; Vaul Drawer reserved for mobile-only bottom-sheet UX
(currently just MoreSheet).

Closes ui/ux M11.

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

src/components/interests/interest-contract-tab.tsx

@@ -22,6 +22,7 @@ import { ExternalEoiUploadDialog } from '@/components/interests/external-eoi-upl
 import { SigningProgress } from '@/components/documents/signing-progress';
 import { apiFetch } from '@/lib/api/client';
 import { toastError } from '@/lib/api/toast-error';
+import { useConfirmation } from '@/hooks/use-confirmation';
 import { cn } from '@/lib/utils';
 import { useUIStore } from '@/stores/ui-store';
 
@@ -197,6 +198,7 @@ function ActiveContractCard({
   onUploadSigned: () => void;
 }) {
   const queryClient = useQueryClient();
+  const { confirm, dialog: confirmDialog } = useConfirmation();
 
   const { data: signersRes, isLoading: signersLoading } = useQuery<{ data: DocumentSigner[] }>({
     queryKey: ['documents', doc.id, 'signers'],
@@ -306,10 +308,13 @@ function ActiveContractCard({
             variant="ghost"
             size="sm"
             disabled={cancelMutation.isPending}
-            onClick={() => {
-              if (window.confirm('Cancel this contract? Signers will no longer be able to sign.')) {
-                cancelMutation.mutate();
-              }
+            onClick={async () => {
+              const ok = await confirm({
+                title: 'Cancel contract',
+                description: 'Signers will no longer be able to sign.',
+                confirmLabel: 'Cancel contract',
+              });
+              if (ok) cancelMutation.mutate();
             }}
             className="h-7 gap-1.5 text-xs text-destructive hover:text-destructive [&_svg]:size-3"
           >
@@ -318,6 +323,7 @@ function ActiveContractCard({
           </Button>
         </div>
       </footer>
+      {confirmDialog}
     </section>
   );
 }