feat: unified Catalog page with Location→Category→Subcategory→Product tree

- New /catalog page with tree view: Location (🌍) → Category (📂) → Subcategory (📁) → Product
- Add/delete locations, categories, subcategories, products from one page
- JS-powered subcategory dropdown filtered by category
- Sticky sidebar with Add Location/Category/Product forms
- Responsive grid layout (tree + forms side by side, stacks on mobile)
- Navigation simplified: Catalog replaces separate Locations/Categories/Products
- Old routes still accessible for backward compatibility
- Subcategories table migration (006_subcategories.js)
- subcategory_id column added to products table
- Seed data includes subcategories (VPN, Accounts, Hardware, etc.)

src/admin/server.js

@@ -5,6 +5,7 @@ import { dirname, join } from 'path';
 import logger from '../utils/logger.js';
 import { requireAuth, handleLogin, handleLogout, renderLogin } from './auth.js';
 import dashboardRouter from './routes/dashboard.js';
+import catalogRouter from './routes/catalog.js';
 import usersRouter from './routes/users.js';
 import productsRouter from './routes/products.js';
 import walletsRouter from './routes/wallets.js';
@@ -13,6 +14,7 @@ import auditRouter from './routes/audit.js';
 import settingsRouter from './routes/settings.js';
 import categoriesRouter from './routes/categories.js';
 import paymentWalletsRouter from './routes/paymentWallets.js';
+import locationsRouter from './routes/locations.js';
 import seedRouter from './routes/seed.js';
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
@@ -36,6 +38,7 @@ app.get('/logout', handleLogout);
 app.use(requireAuth);
 
 app.use('/', dashboardRouter);
+app.use('/catalog', catalogRouter);
 app.use('/users', usersRouter);
 app.use('/products', productsRouter);
 app.use('/wallets', walletsRouter);
@@ -43,6 +46,7 @@ app.use('/purchases', purchasesRouter);
 app.use('/audit', auditRouter);
 app.use('/settings', settingsRouter);
 app.use('/categories', categoriesRouter);
+app.use('/locations', locationsRouter);
 app.use('/payment-wallets', paymentWalletsRouter);
 app.use('/seed', seedRouter);