feat: move transactions page to features module and clean up pages dir

Move TransactionsPage from pages/transactions/ to features/transactions/pages/,
create a feature module index, update App.tsx import to use @/features/transactions,
and remove the now-empty pages/ directory.

Author: bjcoombs

frontend/src/App.tsx

@@ -28,7 +28,7 @@ import { ForecastingPage } from '@/features/forecasting'
 import { DashboardPage } from '@/features/dashboard'
 import { ManifestsPage } from '@/features/manifests'
 import { McpConfigPage } from '@/features/mcp-config'
-import { TransactionsPage } from '@/pages/transactions'
+import { TransactionsPage } from '@/features/transactions'
 
 // Placeholder page components - replaced as each page task is implemented
 function PlaceholderPage({ title }: { title: string }) {

frontend/src/features/transactions/index.ts

@@ -0,0 +1,2 @@
+// Public API for transactions module
+export { TransactionsPage } from './pages/index'