feat(10-02): lead CRUD UI with list, detail, and form components

- /admin/leads list page with LeadTable component (all leads with status badges)
- /admin/leads/[id] detail page with full lead profile and activity log
- LeadForm component for creating/editing leads (modal dialogs)
- Server actions: createLead, updateLead, deleteLead with Zod validation
- Admin sidebar updated to include Lead link
- Added missing UI dependencies: @radix-ui/react-dialog, date-fns, Form component

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/components/admin/AdminSidebar.tsx

@@ -12,11 +12,13 @@ import {
   BookOpen,
   Settings,
   LogOut,
+  Zap,
 } from "lucide-react";
 
 const NAV_ITEMS = [
   { href: "/admin",              label: "Dashboard",    icon: LayoutDashboard, exact: true },
   { href: "/admin/clients",      label: "Clienti",      icon: Users },
+  { href: "/admin/leads",        label: "Lead",         icon: Zap },
   { href: "/admin/projects",     label: "Progetti",     icon: FolderOpen },
   { href: "/admin/offers",       label: "Offerte",      icon: Tag },
   { href: "/admin/forecast",     label: "Forecast",     icon: TrendingUp },