fix(shop): don't treat ContractLockPurchase sentinel 'None' as a real lock

Regression from the contract-lock feature: the check gated on any non-empty
ContractLockPurchase, but the blueprint data uses the string "None" (not "")
for items with no lock (749/773 items). So virtually every item returned
'Item is locked' before the currency deduction -> players couldn't buy anything
(error shown, K-Marks unchanged). Skip the gate when the value is null/empty/"None".

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Prospect.Server.Api/Services/CloudScript/Functions/PurchaseWeaponShopItem.cs

@@ -155,12 +155,14 @@ public class PurchaseWeaponShopItemFunction : ICloudScriptFunction<PurchaseWeapo
         var blueprintData = blueprints[request.BaseItemID];
 
         // Contract unlock criteria: some items can only be purchased after completing a
-        // specific contract. Only gate when the item explicitly declares such a lock, so
-        // items with no lock keep working as before.
-        if (!string.IsNullOrEmpty(blueprintData.UnlockData?.ContractLockPurchase))
+        // specific contract. The data uses the sentinel "None" (not an empty string) for
+        // items with no lock — treat that (and null/empty) as "no lock", otherwise EVERY
+        // item gets gated and nothing can be bought.
+        var contractLockPurchase = blueprintData.UnlockData?.ContractLockPurchase;
+        if (!string.IsNullOrEmpty(contractLockPurchase) && contractLockPurchase != "None")
         {
             var completed = JsonSerializer.Deserialize<FYGetCompletedContractsResult>(userData["ContractsOneTimeCompleted"].Value);
-            if (completed?.ContractsIDs == null || !completed.ContractsIDs.Contains(blueprintData.UnlockData.ContractLockPurchase))
+            if (completed?.ContractsIDs == null || !completed.ContractsIDs.Contains(contractLockPurchase))
             {
                 return new PurchaseWeaponShopItemResponse
                 {