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/components/FooterContentPage.test.ts

@@ -3,8 +3,8 @@ import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 const preferenceState = vi.hoisted(() => ({ language: 'en' as 'en' | 'fr' | 'ar' }))
 
-vi.mock('@/components/MarketplaceShell', () => ({
-  useMarketplacePreferences: () => ({ language: preferenceState.language, theme: 'light' }),
+vi.mock('@/components/StorefrontShell', () => ({
+  useStorefrontPreferences: () => ({ language: preferenceState.language, theme: 'light' }),
 }))
 
 import FooterContentPage from './FooterContentPage'
@@ -29,7 +29,7 @@ describe('FooterContentPage', () => {
     preferenceState.language = 'en'
   })
 
-  it('uses the current marketplace language when no forced language is provided', () => {
+  it('uses the current storefront language when no forced language is provided', () => {
     preferenceState.language = 'fr'
     const page = FooterContentPage({ slug: 'contact-sales' })
     const text = collectText(page).join(' ')