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/leads/LeadForm.tsx

@@ -5,7 +5,7 @@ import { useForm } from "react-hook-form";
 import { zodResolver } from "@hookform/resolvers/zod";
 import { createLeadSchema, LEAD_STAGES, type CreateLeadInput } from "@/lib/lead-validators";
 import { Lead } from "@/db/schema";
-import { createLead, updateLead } from "@/app/admin/leads/actions";
+import { createLead, updateLead } from "@/app/admin/pipeline/actions";
 import {
   Dialog,
   DialogContent,