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/controllers/tenants.controller.ts

@@ -0,0 +1,60 @@
+import { Request, Response, NextFunction } from 'express';
+import * as tenantsService from '../services/tenants.service.js';
+import { AppError } from '../utils/errors.js';
+
+export async function getAllTenants(req: Request, res: Response, next: NextFunction) {
+  try {
+    // Only admin can list all tenants
+    if (req.user!.role !== 'admin') {
+      throw new AppError(403, 'Solo administradores pueden ver todos los clientes');
+    }
+
+    const tenants = await tenantsService.getAllTenants();
+    res.json(tenants);
+  } catch (error) {
+    next(error);
+  }
+}
+
+export async function getTenant(req: Request, res: Response, next: NextFunction) {
+  try {
+    if (req.user!.role !== 'admin') {
+      throw new AppError(403, 'Solo administradores pueden ver detalles de clientes');
+    }
+
+    const tenant = await tenantsService.getTenantById(req.params.id);
+    if (!tenant) {
+      throw new AppError(404, 'Cliente no encontrado');
+    }
+
+    res.json(tenant);
+  } catch (error) {
+    next(error);
+  }
+}
+
+export async function createTenant(req: Request, res: Response, next: NextFunction) {
+  try {
+    if (req.user!.role !== 'admin') {
+      throw new AppError(403, 'Solo administradores pueden crear clientes');
+    }
+
+    const { nombre, rfc, plan, cfdiLimit, usersLimit } = req.body;
+
+    if (!nombre || !rfc) {
+      throw new AppError(400, 'Nombre y RFC son requeridos');
+    }
+
+    const tenant = await tenantsService.createTenant({
+      nombre,
+      rfc,
+      plan,
+      cfdiLimit,
+      usersLimit,
+    });
+
+    res.status(201).json(tenant);
+  } catch (error) {
+    next(error);
+  }
+}