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/app/(dashboard)/subscription/page.tsx

@@ -119,7 +119,7 @@ export default function SubscriptionPage() {
       statusLabels: { TRIALING: 'Trialing', ACTIVE: 'Active', PAST_DUE: 'Past due', CANCELLED: 'Cancelled', UNPAID: 'Unpaid' } as Record<string, string>,
       invoiceStatusLabels: { PAID: 'Paid', PENDING: 'Pending', FAILED: 'Failed', REFUNDED: 'Refunded' } as Record<string, string>,
       planFeatures: {
-        STARTER: ['Up to 10 vehicles', '1 user seat', 'Basic analytics', 'Marketplace listing'],
+        STARTER: ['Up to 10 vehicles', '1 user seat', 'Basic analytics', 'Storefront listing'],
         GROWTH: ['Up to 50 vehicles', '5 user seats', 'Full analytics', 'Priority listing', 'Custom branding'],
         PRO: ['Unlimited vehicles', 'Unlimited seats', 'Advanced reports', 'API access', 'Dedicated support'],
       } as Record<Plan, string[]>,
@@ -162,7 +162,7 @@ export default function SubscriptionPage() {
       statusLabels: { TRIALING: 'Essai', ACTIVE: 'Actif', PAST_DUE: 'En retard', CANCELLED: 'Annulé', UNPAID: 'Impayé' } as Record<string, string>,
       invoiceStatusLabels: { PAID: 'Payé', PENDING: 'En attente', FAILED: 'Échec', REFUNDED: 'Remboursé' } as Record<string, string>,
       planFeatures: {
-        STARTER: ['Jusqu’à 10 véhicules', '1 utilisateur', 'Analyses de base', 'Présence marketplace'],
+        STARTER: ['Jusqu’à 10 véhicules', '1 utilisateur', 'Analyses de base', 'Présence storefront'],
         GROWTH: ['Jusqu’à 50 véhicules', '5 utilisateurs', 'Analyses complètes', 'Mise en avant prioritaire', 'Personnalisation'],
         PRO: ['Véhicules illimités', 'Utilisateurs illimités', 'Rapports avancés', 'Accès API', 'Support dédié'],
       } as Record<Plan, string[]>,