feat: Make TVA and payment method values editable, remove RON currency

- Make payment methods (CARD/NUMERAR) editable InputNumber fields
- Remove RON currency display from TOTAL, TVA, and payment fields
- Allow editing REJECTED receipts (to fix OCR errors before resubmit)
- Add "Editeaza" button for REJECTED receipts in view mode
- Fix null amount validation by converting to 0 before API call

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

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

data-entry-app/backend/app/db/crud/receipt.py

@@ -254,11 +254,11 @@ class ReceiptCRUD:
     @staticmethod
     async def can_edit(receipt: Receipt, username: str) -> bool:
         """Check if user can edit receipt."""
-        # Only DRAFT receipts can be edited
-        if receipt.status != ReceiptStatus.DRAFT:
+        # DRAFT and REJECTED receipts can be edited (to fix and resubmit)
+        if receipt.status not in [ReceiptStatus.DRAFT, ReceiptStatus.REJECTED]:
             return False
 
-        # Only creator can edit their own drafts
+        # Only creator can edit their own receipts
         return receipt.created_by == username
 
     @staticmethod