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/components/admin/dashboard/FollowUpWidget.tsx

@@ -47,7 +47,7 @@ export async function FollowUpWidget() {
           </span>
         </div>
         <Link
-          href="/admin/leads"
+          href="/admin/pipeline"
           className="text-xs font-medium text-[#71717a] hover:text-[#1A463C] transition-colors"
         >
           Vedi tutti →
@@ -59,7 +59,7 @@ export async function FollowUpWidget() {
         {visible.map((lead) => (
           <li key={lead.id}>
             <Link
-              href={`/admin/leads/${lead.id}`}
+              href={`/admin/pipeline/${lead.id}`}
               className="flex items-center gap-3 px-5 py-3 hover:bg-[#f9f9f9] transition-colors group"
             >
               <span className="flex h-9 w-9 shrink-0 items-center justify-center rounded-full bg-[#1A463C]/10 text-[#1A463C] text-xs font-bold">
@@ -85,7 +85,7 @@ export async function FollowUpWidget() {
 
       {leads.length > MAX_ROWS && (
         <Link
-          href="/admin/leads"
+          href="/admin/pipeline"
           className="block px-5 py-2.5 text-center text-xs font-medium text-[#71717a] hover:text-[#1A463C] border-t border-[#f4f4f5] transition-colors"
         >
           Vedi tutti i {leads.length} lead