feat: add receipt upload functionality for Einnahmen and Beleg routes

- Implemented upload and retrieval of receipts (Belege) associated with Einnahmen entries.
- Added new API routes for uploading and deleting receipts.
- Updated the Einnahmen model to include a `belegUrl` field for storing receipt references.
- Enhanced the Einnahmen page to support file uploads and display existing receipts.
- Introduced drag-and-drop functionality for file uploads and improved user feedback during uploads.
- Added necessary validation for file types and sizes during uploads.

app/lib/logger.server.ts

@@ -21,7 +21,9 @@ export type LogAction =
   | "DELETE_CUSTOMER"
   | "CREATE_SERVICE"
   | "UPDATE_SERVICE"
-  | "DELETE_SERVICE";
+  | "DELETE_SERVICE"
+  | "UPLOAD_BELEG"
+  | "DELETE_BELEG";
 
 export async function log({
   userId,