Add main menu page with role-based modules (#7)

- `/` is now the main menu; orders/receipts page moved to `/receipts`
- Module registry (features/menu/modules.ts) drives both the menu tiles
  and route guards (ModuleRoute); admin sees every module
- Menu: module search with Ctrl+K, profile with logout, responsive grid,
  palette matching the login page
- «← Головне меню» link on receipts and cash registers pages;
  «Каси» moved from the receipts toolbar into the menu

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/pages/DashboardPage.tsx

@@ -5,6 +5,7 @@ import { Link } from 'react-router-dom'
 import { deleteOrder } from '@/api/orders'
 import { cancelReceipt, createReceipts } from '@/api/receipts'
 import '@/pages/DashboardPage.css'
+import { ROLE_LABEL } from '@/features/auth/roles'
 import { useAuth } from '@/features/auth/useAuth'
 import { OrderDetailModal } from '@/features/orders/OrderDetailModal'
 import type { Order, OrderTab } from '@/features/orders/types'
@@ -13,12 +14,6 @@ import { defaultPrepayment, prepaymentMatches, toKopecks } from '@/features/rece
 import { CANCELLABLE, RECEIPT_STATUS } from '@/features/receipts/types'
 import type { ReceiptRequestItem } from '@/features/receipts/types'
 
-const ROLE_LABEL: Record<string, string> = {
-  admin: 'Адміністратор',
-  cashier: 'Касир',
-  viewer: 'Спостерігач',
-}
-
 const TABS: { key: OrderTab; label: string }[] = [
   { key: 'no_receipt', label: 'Без чека' },
   { key: 'has_receipt', label: 'Виписані чеки' },
@@ -174,10 +169,15 @@ export function DashboardPage() {
   return (
     <div className="dashboard-shell">
       <header className="dashboard-topbar">
-        <span className="dashboard-brand">Assistant System</span>
+        <div className="dashboard-topbar-start">
+          <Link to="/" className="orders-link-btn">
+            ← Головне меню
+          </Link>
+          <span className="dashboard-brand">Assistant System</span>
+        </div>
         <div className="dashboard-user">
           <span>{user?.full_name}</span>
-          <span className="dashboard-role">{user ? (ROLE_LABEL[user.role] ?? user.role) : ''}</span>
+          <span className="dashboard-role">{user ? ROLE_LABEL[user.role] : ''}</span>
           <button type="button" className="dashboard-logout" onClick={() => void logout()}>
             Вийти
           </button>
@@ -188,11 +188,6 @@ export function DashboardPage() {
         <div className="orders-toolbar">
           <h2>Замовлення</h2>
           <div className="orders-toolbar-actions">
-            {user?.role === 'admin' && (
-              <Link to="/cash-registers" className="orders-link-btn">
-                Каси
-              </Link>
-            )}
             {tab === 'no_receipt' && canFiscalize && (
               <button
                 type="button"