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/CashRegistersPage.tsx

@@ -1,7 +1,7 @@
 import { useQuery, useQueryClient } from '@tanstack/react-query'
 import { useState } from 'react'
 import type { FormEvent } from 'react'
-import { Link, Navigate } from 'react-router-dom'
+import { Link } from 'react-router-dom'
 
 import {
   checkCashRegister,
@@ -55,8 +55,6 @@ export function CashRegistersPage() {
   const [busy, setBusy] = useState(false)
   const [message, setMessage] = useState<{ tone: 'ok' | 'error'; text: string } | null>(null)
 
-  if (user && user.role !== 'admin') return <Navigate to="/" replace />
-
   async function run(action: () => Promise<unknown>, okText: string) {
     setBusy(true)
     try {
@@ -123,10 +121,12 @@ export function CashRegistersPage() {
   return (
     <div className="dashboard-shell">
       <header className="dashboard-topbar">
-        <span className="dashboard-brand">Assistant System</span>
-        <Link to="/" className="orders-link-btn">
-          ← До замовлень
-        </Link>
+        <div className="dashboard-topbar-start">
+          <Link to="/" className="orders-link-btn">
+            ← Головне меню
+          </Link>
+          <span className="dashboard-brand">Assistant System</span>
+        </div>
       </header>
 
       <main className="orders-body">