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/dashboard/src/lib/urls.test.ts

@@ -27,7 +27,7 @@ afterEach(() => {
 })
 
 describe('dashboard cross-app URLs', () => {
-  it('uses default marketplace and admin bases on the server', async () => {
+  it('uses default storefront and admin bases on the server', async () => {
     const { storefrontUrl, adminUrl } = await loadUrls()
 
     expect(storefrontUrl).toBe('http://localhost:3000')
@@ -54,11 +54,11 @@ describe('dashboard cross-app URLs', () => {
 
   it('preserves non-URL values after normalizing their trailing slash', async () => {
     const { storefrontUrl, adminUrl } = await loadUrls({
-      NEXT_PUBLIC_STOREFRONT_URL: '/marketplace/',
+      NEXT_PUBLIC_STOREFRONT_URL: '/storefront/',
       NEXT_PUBLIC_ADMIN_URL: '/admin/',
     })
 
-    expect(storefrontUrl).toBe('/marketplace')
+    expect(storefrontUrl).toBe('/storefront')
     expect(adminUrl).toBe('/admin')
   })
 })