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/mock/client.ts

@@ -236,7 +236,7 @@ export class MockGateway implements GatewayClient {
     return { orderId: 'mock-order-' + productId, redirectUrl: 'https://mock.local/robokassa?order=' + productId };
   }
 
-  async walletReward(_nonce: string, _diag: string): Promise<Wallet> {
+  async walletReward(_nonce: string): Promise<Wallet> {
     // Mock rewarded credit: add the configured payout to the vk segment (no cap in the mock).
     const vk = this.mockWallet.segments.find((s) => s.source === 'vk');
     if (vk) vk.chips += this.mockWallet.rewardChips;