feat(client-groups): CM-1 API routes + UI (list, member viewer, copy-emails)

- /api/v1/client-groups (list/create), /[id] (get/patch/delete),
  /[id]/members (get/set) — route.ts + handlers.ts split, client_groups perms
- Client Groups list page (grid + create dialog) and detail page
  (member viewer, per-row copy email, "Copy all emails" → To:-bar format,
  manage-members picker over /api/v1/clients)
- Sidebar nav entry (UsersRound icon)

tsc clean, lint 0 errors, prod build green. Completes CM-1 (Mailchimp push
still deferred until client creds/account).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app/(dashboard)/[portSlug]/client-groups/[groupId]/page.tsx

@@ -0,0 +1,10 @@
+import { ClientGroupDetail } from '@/components/client-groups/client-group-detail';
+
+export default async function ClientGroupDetailPage({
+  params,
+}: {
+  params: Promise<{ portSlug: string; groupId: string }>;
+}) {
+  const { groupId } = await params;
+  return <ClientGroupDetail groupId={groupId} />;
+}

src/app/(dashboard)/[portSlug]/client-groups/page.tsx

@@ -0,0 +1,5 @@
+import { ClientGroupsList } from '@/components/client-groups/client-groups-list';
+
+export default function ClientGroupsPage() {
+  return <ClientGroupsList />;
+}