refactor: rename marketplace to storefront across the entire monorepo

Comprehensive rename of all marketplace references to storefront:
- API module: apps/api/src/modules/marketplace/ → storefront/
- Components: MarketplaceHeader → StorefrontHeader, MarketplaceShell →
  StorefrontShell, MarketplaceFooter → StorefrontFooter
- Types: marketplace-homepage.ts → storefront-homepage.ts
- Test files: employee-marketplace-* → employee-storefront-*
- All source code identifiers, imports, route paths, and strings
- Documentation (docs/), CI config (.gitlab-ci.yml), scripts
- Dashboard, admin, storefront workspace references
- Prisma field names preserved (isListedOnMarketplace, marketplaceRating,
  marketplaceFunnelEvent) as they map to database schema

Validation:
- API type-check: 0 errors
- Storefront type-check: 0 errors
- Dashboard type-check: 0 errors
- Full monorepo type-check: only pre-existing admin TS18046

apps/admin/src/app/dashboard/companies/[id]/page.tsx

@@ -724,7 +724,7 @@ export default function AdminCompanyDetailPage() {
             </label>
             <label className="flex items-center gap-3 pt-7 text-sm text-zinc-300">
               <input type="checkbox" checked={form.brand.isListedOnMarketplace} onChange={(e) => updateSection('brand', { isListedOnMarketplace: e.target.checked })} />
-              Listed on marketplace
+              Listed on storefront
             </label>
           </div>
         </section>