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.ts

@@ -3,7 +3,7 @@ import { AppError, NotFoundError } from '../../http/errors'
 import { getVehicleAvailabilitySummary } from '../../services/vehicleAvailabilityService'
 import { applyPricingRules } from '../../services/pricingRuleService'
 import { validateLicense } from '../../services/licenseValidationService'
-import { getMarketplaceHomepageContent } from '../../services/platformContentService'
+import { getStorefrontHomepageContent } from '../../services/platformContentService'
 import { prisma } from '../../lib/prisma'
 import * as amanpay from '../../services/amanpayService'
 import * as paypal from '../../services/paypalService'
@@ -53,7 +53,7 @@ function generateBookingReference() {
 }
 
 export async function getPlatformHomepage() {
-  return getMarketplaceHomepageContent()
+  return getStorefrontHomepageContent()
 }
 
 export async function getPlatformPricing() {