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

storefront/src/components/public/SiteFooter.tsx

@@ -1,4 +1,4 @@
 'use client'
 
 // Public marketing footer used by the homepage and other storefront pages.
-export { default } from '@/components/MarketplaceFooter'
+export { default } from '@/components/StorefrontFooter'

storefront/src/components/public/SiteNavbar.tsx

@@ -1,4 +1,4 @@
 'use client'
 
 // Public marketing navbar used by the homepage and other storefront pages.
-export { default } from '@/components/MarketplaceHeader'
+export { default } from '@/components/StorefrontHeader'

storefront/src/components/public/SitePageLayout.tsx

@@ -7,12 +7,12 @@ import SiteNavbar from './SiteNavbar'
 import {
   getFooterContent,
   localeOptions,
-  useMarketplacePreferences,
-} from '@/components/MarketplaceShell'
+  useStorefrontPreferences,
+} from '@/components/StorefrontShell'
 import { resolveBrowserAppUrl } from '@/lib/appUrls'
 
 export default function SitePageLayout({ children }: { children: ReactNode }) {
-  const { language, theme, dict, companyName, setLanguage, setTheme } = useMarketplacePreferences()
+  const { language, theme, dict, companyName, setLanguage, setTheme } = useStorefrontPreferences()
   const dashboardUrl = resolveBrowserAppUrl(
     process.env.NEXT_PUBLIC_DASHBOARD_URL ?? 'http://localhost:3000/dashboard',
   )