fix(icons): migrate Marketplace Builder to Lucide

Replace every PrimeIcons pi-* usage across the builder: overview page
(back link, next-step arrow, section cards, readiness checklist,
quick links), sidebar nav (group/section status dots), main layout
(back/home/menu/help icons), brand + homepage overview panels
(checklist ok/pending dots, contrast warning), footer/homepage/widgets
section editors (drag handles, move up/down, duplicate, remove), and
the HTML editor toolbar (list/link/image/table/divider/code/embed).

Notable correctness fix: PrimeIcons reused pi-bars for both the
hamburger menu toggle AND every drag handle - two different meanings
sharing one icon (exactly the kind of icon collision the audit calls
out). Added a dedicated 'grip' icon (GripVertical) for drag handles so
menu and drag-to-reorder are visually distinct.

Added a global .spin utility (icon-registry has no built-in spinner
animation) for the one loading-spinner icon in the builder overview
checklist.

All icon-bearing fields (BuilderGroup.icon, BlockCatalogEntry.icon,
WIDGET_ICONS, STATUS_ICON, HtmlEditorToolbarCommand.icon, etc.) are
now typed AppIconName instead of string.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/styles.scss

@@ -140,6 +140,15 @@ a, button, input, textarea, select {
   outline-offset: 2px;
 }
 
+/* Spinner rotation for app-icon name="spinner" used as a loading indicator */
+@keyframes app-icon-spin {
+  to { transform: rotate(360deg); }
+}
+
+.spin {
+  animation: app-icon-spin 1s linear infinite;
+}
+
 /* Respect OS-level reduced-motion preference globally: neutralizes hover
    transforms, card-entrance/skeleton-shimmer animations, and smooth-scroll
    everywhere in one place rather than requiring every component to opt in