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/api/src/modules/site/site.service.boundary.test.ts

@@ -10,7 +10,7 @@ vi.mock('../../lib/prisma', () => ({
     planFeature: { findMany: vi.fn() },
   },
 }))
-vi.mock('../../services/platformContentService', () => ({ getMarketplaceHomepageContent: vi.fn() }))
+vi.mock('../../services/platformContentService', () => ({ getStorefrontHomepageContent: vi.fn() }))
 vi.mock('../../services/vehicleAvailabilityService', () => ({ getVehicleAvailabilitySummary: vi.fn() }))
 vi.mock('../../services/insuranceService', () => ({ applyInsurancesToReservation: vi.fn() }))
 vi.mock('../../services/additionalDriverService', () => ({ applyAdditionalDriversToReservation: vi.fn() }))