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

docs/CAR_BOOKING_PROCESS_IMPROVEMENT_PLAN.md

@@ -28,7 +28,7 @@ This reduces cognitive load, reduces privacy anxiety, and makes mobile completio
 
 Replace the current booking form with the revised version in:
 
-`apps/marketplace/src/components/BookingForm.tsx`
+`apps/storefront/src/components/BookingForm.tsx`
 
 Acceptance criteria:
 
@@ -50,7 +50,7 @@ Recommended behavior:
 
 Backend candidate:
 
-- Add or expose `GET /marketplace/:slug/vehicles/:id/availability?startDate=&endDate=`.
+- Add or expose `GET /storefront/:slug/vehicles/:id/availability?startDate=&endDate=`.
 - Reuse the existing `getVehicleAvailabilitySummary` service instead of inventing yet another inconsistent truth source, because apparently systems enjoy lying to themselves.
 
 ### Phase 3: Booking Status Transparency