feat(messaging): Add broadcast messaging system for owners and managers

- Add BroadcastMessage and MessageRecipient models for sending messages to groups or individuals
- Add Messages page with compose form and sent messages list
- Support targeting by role (owners, managers, staff, customers) or individual users
- Add can_send_messages permission (owners always, managers by default with revocable permission)
- Add autofill search dropdown with infinite scroll for selecting individual recipients
- Add staff permission toggle for managers' messaging access
- Integrate Messages link in sidebar for users with permission

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/App.tsx

@@ -41,6 +41,7 @@ const Scheduler = React.lazy(() => import('./pages/Scheduler'));
 const Customers = React.lazy(() => import('./pages/Customers'));
 const Settings = React.lazy(() => import('./pages/Settings'));
 const Payments = React.lazy(() => import('./pages/Payments'));
+const Messages = React.lazy(() => import('./pages/Messages'));
 const Resources = React.lazy(() => import('./pages/Resources'));
 const Services = React.lazy(() => import('./pages/Services'));
 const Staff = React.lazy(() => import('./pages/Staff'));
@@ -861,11 +862,8 @@ const AppContent: React.FC = () => {
             <Route
               path="/messages"
               element={
-                hasAccess(['owner', 'manager']) ? (
-                  <div className="p-8">
-                    <h1 className="text-2xl font-bold mb-4">Messages</h1>
-                    <p className="text-gray-600">Messages feature coming soon...</p>
-                  </div>
+                hasAccess(['owner', 'manager']) && user?.can_send_messages ? (
+                  <Messages />
                 ) : (
                   <Navigate to="/" />
                 )