fix(payments): VK-iOS freeze is purchase-only; remove the rewarded diagnostic

Testing the rewarded slice surfaced a contradiction: rewarded ads let a VK-iOS
user earn vk chips, but the blanket VK-iOS "spend freeze" then blocked spending
them (the wallet showed "5 (view-only)"). Apple's ToS forbids only BUYING in-app
values on VK-iOS (money -> chips), not spending or earning them — so the freeze is
corrected to purchase-only: vkFrozen() now gates only CreateOrder (the money-in
step), not spendableSources (spending). VK-wallet chips — earned via rewarded ads
or bought on the same account elsewhere (VK Android) — now spend on VK-iOS too.
(Owner's ToS finding.)

Also: the temporary contour diagnostic confirmed VK returns only {result:true} for
a rewarded view (no token/signature) — client-attested is final, no hardening
possible — so the diagnostic (the log and the diag wire field) is removed.

Docs: PAYMENTS(+ru) VK-iOS freeze + D17 amend + PLAN E6. Tests updated (gate /
wallet VK-iOS now spendable).

ui/src/lib/transport.ts

@@ -240,8 +240,8 @@ export function createTransport(baseUrl: string): GatewayClient {
     async walletOrder(productId: string) {
       return codec.decodeWalletOrder(await exec('wallet.order', codec.encodeWalletOrder(productId)));
     },
-    async walletReward(nonce: string, diag: string) {
-      return codec.decodeWallet(await exec('wallet.reward', codec.encodeWalletReward(nonce, diag)));
+    async walletReward(nonce: string) {
+      return codec.decodeWallet(await exec('wallet.reward', codec.encodeWalletReward(nonce)));
     },
 
     async friendsList() {