Fix json import scope issue in process_payment function

The json import was inside a conditional block but needed later in the function.
Moved import to top of function to fix UnboundLocalError.

All crypto_watcher and double_spend_protection tests now pass.

make_post_sell/lib/crypto_watcher.py

@@ -1007,6 +1007,8 @@ def process_payment(
 
     Mirrors the status and finalization logic for easier unit testing.
     """
+    import json
+
     now_ms = int(time.time() * 1000)
 
     # Initialize payment rescue if client is available
@@ -1039,8 +1041,6 @@ def process_payment(
         # For duplicate payments, we need to look up the specific transaction since
         # incoming_transfers only contains current scanning window
         if crypto_payment.tx_hashes and payment_rescue and refund_address:
-            import json
-
             try:
                 stored_txids = json.loads(crypto_payment.tx_hashes or "[]")
                 if stored_txids and client: