feat: Quiet Luxury design system + Pipeline (ex-Lead) redesign

- Design system foundations: Plus Jakarta Sans font, shadow-card/radius
  tokens in @theme, design-reference/DESIGN-SYSTEM.md with component inventory
- Collapsible admin shell (AdminShell): smooth w-64<->w-20 sidebar, new top
  header with "Admin" + avatar placeholder, localStorage-persisted state
- Rename route /admin/leads -> /admin/pipeline (redirect stubs preserved),
  nav label Lead -> Pipeline; DB table unchanged
- Reusable primitives: StatusBadge, SearchInput, SegmentedToggle (dual-theme)
- Luxury restyle of lead table, kanban (6 stages + @dnd-kit intact), PageHeader
- Tokenize editable-cell / option-multi-select for dark-mode legibility

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/admin/pipeline/page.tsx

@@ -0,0 +1,24 @@
+import { getLeadsWithTags, getLeadFieldOptions } from "@/lib/admin-queries";
+import { LeadsViewToggle } from "@/components/admin/leads/LeadsViewToggle";
+import { CreateLeadModal } from "@/components/admin/leads/LeadForm";
+import { PageHeader } from "@/components/admin/PageHeader";
+
+export const revalidate = 0;
+
+export default async function LeadsPage() {
+  const [leads, options] = await Promise.all([
+    getLeadsWithTags(),
+    getLeadFieldOptions(),
+  ]);
+
+  return (
+    <div className="space-y-6">
+      <PageHeader
+        title="Lead Pipeline"
+        subtitle="Gestisci e monitora i tuoi contatti commerciali"
+        action={<CreateLeadModal />}
+      />
+      <LeadsViewToggle leads={leads} options={options} />
+    </div>
+  );
+}