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/app/globals.css

@@ -109,7 +109,7 @@
 
 @theme inline {
   /* Font */
-  --font-sans: var(--font-geist-sans), system-ui, -apple-system, BlinkMacSystemFont,
+  --font-sans: var(--font-plus-jakarta-sans), system-ui, -apple-system, BlinkMacSystemFont,
     "Segoe UI", Roboto, "Helvetica Neue", sans-serif;
   --font-mono: var(--font-geist-mono);
 
@@ -149,6 +149,16 @@
   --color-tertiary: var(--tertiary);
   --color-bg-subtle: var(--bg-subtle);
   --color-border-light: var(--border-light);
+
+  /* Radius — wire the base --radius into Tailwind's radius scale so
+     rounded-lg / rounded-xl resolve off a single token. */
+  --radius-lg: var(--radius);
+  --radius-xl: calc(var(--radius) + 0.25rem);
+
+  /* Luxury shadows — very low-opacity, wide-spread card elevation
+     ("Quiet Luxury" design system). */
+  --shadow-card: 0 4px 20px rgba(0, 0, 0, 0.01);
+  --shadow-card-hover: 0 8px 30px rgba(0, 0, 0, 0.02);
 }
 
 /* =========================================================