feat: ConnectWise PSA integration (#106)

PSA abstraction layer with provider pattern, ConnectWise integration (connection management, ticket linking, note posting, status updates, member mapping), Integrations page UI, Fernet credential encryption, in-memory TTL cache, 6 DB migrations, ConnectWise API reference docs.

frontend/src/router.tsx

@@ -68,6 +68,7 @@ const ProfileSettingsPage = lazy(() => import('@/pages/account/ProfileSettingsPa
 const TeamCategoriesPage = lazy(() => import('@/pages/account/TeamCategoriesPage'))
 const TargetListsPage = lazy(() => import('@/pages/account/TargetListsPage'))
 const ChatRetentionSettingsPage = lazy(() => import('@/pages/account/ChatRetentionSettingsPage'))
+const IntegrationsPage = lazy(() => import('@/pages/account/IntegrationsPage'))
 
 /** Wraps a lazy-loaded page with Suspense + ErrorBoundary */
 function page(Component: React.LazyExoticComponent<React.ComponentType>) {
@@ -224,6 +225,14 @@ export const router = sentryCreateBrowserRouter([
             ),
           },
           { path: 'target-lists', element: page(TargetListsPage) },
+          {
+            path: 'integrations',
+            element: (
+              <ProtectedRoute requiredRole="owner">
+                {page(IntegrationsPage)}
+              </ProtectedRoute>
+            ),
+          },
         ],
       },
     ],