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

.gitlab-ci.yml

@@ -28,14 +28,14 @@ api_tests:
     - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
     - if: '$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH'
 
-marketplace_tests:
+storefront_tests:
   stage: test
   image: node:20-bookworm
   before_script:
     - npm ci
     - npm run build --workspace @rentaldrivego/types
   script:
-    - npm run test:marketplace
+    - npm run test:storefront
   rules:
     - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
     - if: '$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH'