feat(contracts): Add contracts permission to subscription tiers

- Add contracts_enabled field to SubscriptionPlan model
- Add contracts toggle to plan create/edit modal in platform settings
- Hide contracts menu item for tenants without contracts permission
- Protect /contracts routes with canUse('contracts') check
- Add HasContractsPermission to contracts API ViewSets
- Add contracts to PlanPermissions interface and feature definitions

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

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

frontend/src/App.tsx

@@ -9,6 +9,7 @@ import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
 import { useCurrentUser, useMasquerade, useLogout } from './hooks/useAuth';
 import { useCurrentBusiness } from './hooks/useBusiness';
 import { useUpdateBusiness } from './hooks/useBusiness';
+import { usePlanFeatures } from './hooks/usePlanFeatures';
 import { setCookie } from './utils/cookies';
 
 // Import Login Page
@@ -192,6 +193,7 @@ const AppContent: React.FC = () => {
   const updateBusinessMutation = useUpdateBusiness();
   const masqueradeMutation = useMasquerade();
   const logoutMutation = useLogout();
+  const { canUse } = usePlanFeatures();
 
   // Apply dark mode class and persist to localStorage
   React.useEffect(() => {
@@ -810,7 +812,7 @@ const AppContent: React.FC = () => {
             <Route
               path="/contracts"
               element={
-                hasAccess(['owner', 'manager']) ? (
+                hasAccess(['owner', 'manager']) && canUse('contracts') ? (
                   <Contracts />
                 ) : (
                   <Navigate to="/" />
@@ -820,7 +822,7 @@ const AppContent: React.FC = () => {
             <Route
               path="/contracts/templates"
               element={
-                hasAccess(['owner', 'manager']) ? (
+                hasAccess(['owner', 'manager']) && canUse('contracts') ? (
                   <ContractTemplates />
                 ) : (
                   <Navigate to="/" />