feat(clients): selective bulk attach + new bulk detach

Inbounds page:
- AttachClientsModal now shows a per-client selection table (email,
  comment, enabled tag) with search and a live "selected of total"
  counter; all clients are pre-selected so the old "attach all"
  workflow stays a single OK click.
- New DetachClientsModal on the inbound row menu lets you pick which
  clients to remove from that inbound (records are kept so they can be
  re-attached later; for full removal use Delete).

Clients page:
- New "Attach (N)" bulk-action button + BulkAttachInboundsModal that
  attaches selected clients to one or more multi-user inbounds.
- New "Detach (N)" bulk-action button + BulkDetachInboundsModal that
  removes selected clients from chosen inbounds; (email, inbound) pairs
  where the client isn't attached are silently skipped.

Backend adds POST /panel/api/clients/bulkDetach, wrapping the existing
Detach service for each email and reporting per-email
detached/skipped/errors. ClientRecord rows are kept on detach to match
the single-client endpoint; bulkDel remains the path for full removal.

frontend/src/pages/inbounds/InboundsPage.tsx

@@ -39,6 +39,7 @@ const InboundFormModal = lazy(() => import('./InboundFormModal'));
 const InboundInfoModal = lazy(() => import('./InboundInfoModal'));
 const QrCodeModal = lazy(() => import('./QrCodeModal'));
 const AttachClientsModal = lazy(() => import('./AttachClientsModal'));
+const DetachClientsModal = lazy(() => import('./DetachClientsModal'));
 const AssignClientsGroupModal = lazy(() => import('./AssignClientsGroupModal'));
 
 type RowAction =
@@ -52,6 +53,7 @@ type RowAction =
   | 'resetTraffic'
   | 'delAllClients'
   | 'attachClients'
+  | 'detachClients'
   | 'assignGroup'
   | 'clone';
 
@@ -127,6 +129,8 @@ export default function InboundsPage() {
 
   const [attachOpen, setAttachOpen] = useState(false);
   const [attachSource, setAttachSource] = useState<DBInbound | null>(null);
+  const [detachOpen, setDetachOpen] = useState(false);
+  const [detachSource, setDetachSource] = useState<DBInbound | null>(null);
 
   const [groupOpen, setGroupOpen] = useState(false);
   const [groupSource, setGroupSource] = useState<DBInbound | null>(null);
@@ -489,6 +493,10 @@ export default function InboundsPage() {
         setAttachSource(target);
         setAttachOpen(true);
         break;
+      case 'detachClients':
+        setDetachSource(target);
+        setDetachOpen(true);
+        break;
       case 'assignGroup':
         setGroupSource(target);
         setGroupOpen(true);
@@ -614,6 +622,14 @@ export default function InboundsPage() {
             dbInbounds={dbInbounds}
           />
         </LazyMount>
+        <LazyMount when={detachOpen}>
+          <DetachClientsModal
+            open={detachOpen}
+            onClose={() => setDetachOpen(false)}
+            onDetached={refresh}
+            source={detachSource}
+          />
+        </LazyMount>
         <LazyMount when={groupOpen}>
           <AssignClientsGroupModal
             open={groupOpen}