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/LeadDetail.tsx

@@ -13,7 +13,7 @@ import {
   renameLeadTag,
   deleteTranscript,
   convertLeadToClient,
-} from "@/app/admin/leads/actions";
+} from "@/app/admin/pipeline/actions";
 import { formatDistanceToNow, format } from "date-fns";
 import { it } from "date-fns/locale";
 import Link from "next/link";