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/storefront/src/lib/i18n.server.test.ts

@@ -11,31 +11,31 @@ vi.mock('next/headers', () => ({
   }),
 }))
 
-import { getMarketplaceLanguage } from './i18n.server'
+import { getStorefrontLanguage } from './i18n.server'
 import { MARKETPLACE_LANGUAGE_COOKIE, SHARED_LANGUAGE_COOKIE } from './i18n'
 
-describe('getMarketplaceLanguage', () => {
+describe('getStorefrontLanguage', () => {
   beforeEach(() => {
     cookieValues.clear()
   })
 
-  it('prefers the shared language cookie over the legacy marketplace cookie', async () => {
+  it('prefers the shared language cookie over the legacy storefront cookie', async () => {
     cookieValues.set(SHARED_LANGUAGE_COOKIE, 'ar')
     cookieValues.set(MARKETPLACE_LANGUAGE_COOKIE, 'fr')
 
-    await expect(getMarketplaceLanguage()).resolves.toBe('ar')
+    await expect(getStorefrontLanguage()).resolves.toBe('ar')
   })
 
-  it('falls back to the legacy marketplace cookie during migration', async () => {
+  it('falls back to the legacy storefront cookie during migration', async () => {
     cookieValues.set(MARKETPLACE_LANGUAGE_COOKIE, 'fr')
 
-    await expect(getMarketplaceLanguage()).resolves.toBe('fr')
+    await expect(getStorefrontLanguage()).resolves.toBe('fr')
   })
 
   it('defaults to English when cookies are absent or invalid', async () => {
-    await expect(getMarketplaceLanguage()).resolves.toBe('en')
+    await expect(getStorefrontLanguage()).resolves.toBe('en')
     cookieValues.set(SHARED_LANGUAGE_COOKIE, 'es')
 
-    await expect(getMarketplaceLanguage()).resolves.toBe('en')
+    await expect(getStorefrontLanguage()).resolves.toBe('en')
   })
 })