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/codec.test.ts

@@ -78,12 +78,11 @@ describe('codec', () => {
     expect(w.rewardChips).toBe(7);
   });
 
-  it('round-trips the wallet reward request (nonce + diag)', () => {
+  it('round-trips the wallet reward request (nonce)', () => {
     const req = fb.WalletRewardRequest.getRootAsWalletRewardRequest(
-      new ByteBuffer(encodeWalletReward('nonce-9', '{"result":true}')),
+      new ByteBuffer(encodeWalletReward('nonce-9')),
     );
     expect(req.nonce()).toBe('nonce-9');
-    expect(req.diag()).toBe('{"result":true}');
   });
 
   it('round-trips the wallet order request and response', () => {