feat(10-redo-C): CRM leads module — schema, services, UI (Phase 10 redo)

Stage C of staged Phase 10 redo. Restores dangling phase10-wip work:
- schema.ts: leads expansion + activities/reminders tables + relations
- lead-service.ts / lead-validators.ts service layer
- /admin/leads list + detail + actions, LeadTable/LeadDetail/LeadForm
- LogActivityModal, SendQuoteModal, FollowUpWidget on dashboard
- migration 0005 (applied to prod DB in Stage B, along with
  previously-missing 0001/0003/0004 — root cause of all post-deploy
  500s: prod DB had no migrations applied since 0000)

Co-Authored-By: Claude Fable 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 },