feat: add multi-tenant client management for admins

- Add tenants API endpoints (list, get, create)
- Add tenant middleware override via X-View-Tenant header
- Add TenantSelector dropdown component in header
- Add tenant view store with persistence
- Add Clientes management page
- Update all navigation layouts with Clientes link for admins

Admins can now:
- View list of all clients
- Create new clients with automatic schema setup
- Switch between viewing different clients' data
- See which client they are currently viewing

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/src/middlewares/tenant.middleware.ts

@@ -6,6 +6,7 @@ declare global {
   namespace Express {
     interface Request {
       tenantSchema?: string;
+      viewingTenantId?: string;
     }
   }
 }
@@ -16,8 +17,18 @@ export async function tenantMiddleware(req: Request, res: Response, next: NextFu
   }
 
   try {
+    // Check if admin is viewing a different tenant
+    const viewTenantId = req.headers['x-view-tenant'] as string | undefined;
+    let tenantId = req.user.tenantId;
+
+    // Only admins can view other tenants
+    if (viewTenantId && req.user.role === 'admin') {
+      tenantId = viewTenantId;
+      req.viewingTenantId = viewTenantId;
+    }
+
     const tenant = await prisma.tenant.findUnique({
-      where: { id: req.user.tenantId },
+      where: { id: tenantId },
       select: { schemaName: true, active: true },
     });