- product-config.ts: add getRequestProductId(req) helper + KNOWN_PRODUCTS list
- product-context.tsx: new React context storing selected productId in localStorage
- product-switcher.tsx: dropdown component with icons for all 4 products
- api.ts: pass x-product-id header from localStorage on all API calls
- providers.tsx: wrap with ProductProvider
- sidebar-nav.tsx: render ProductSwitcher between logo and nav
- repositories/users.ts + tokens.ts: accept optional productId parameter
- 8 API routes updated: users, auth/login, auth/forgot-password, seed,
settings/plans, themes/active, analytics/retention, analytics/revenue
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