feat(payments): chip wallet, store-compliance gate and benefit application

Stand up the internal chip/benefit mechanic behind the narrow payments interface:
context-aware balances and benefits, an atomic chip spend, admin grants as
zero-price value sales, the one-directional store-compliance gate (VK/TG same-
origin only, web draws direct→vk→tg, VK-iOS frozen, untrusted fail-closed), and
per-origin hint and no-ads application with term stacking. Reads are served from
an in-process, account-keyed write-through cache (mirroring the suspension gate),
so hot paths issue no query to the payments schema.

Flip the online-game hint wallet and the ad-banner suppression from the deprecated
accounts.hint_balance / paid_account columns to the payments benefit (a hint
balance no longer suppresses the banner — only a no-ads benefit does), and fold
chip segments and benefits by origin on account merge, inside the merge tx. Add
the GET/POST /api/v1/user/wallet edge chain (REST → Connect → FlatBuffers) plus
its codec unit test; no wallet UI yet.

Bring the frozen owner decisions log into the repo at
docs/PAYMENTS_DECISIONS_ru.md (it was untracked under .vscode) and reference it
from PLAN.md; record the read-cache design and the present-sources interface in
PLAN.md and docs/PAYMENTS.md (+ RU mirror).

ui/src/lib/codec.ts

@@ -38,6 +38,8 @@ import type {
   MoveRecord,
   MoveResult,
   Profile,
+  Wallet,
+  WalletSegment,
   ProfileUpdate,
   PushEvent,
   Seat,
@@ -359,6 +361,33 @@ export function decodeSession(buf: Uint8Array): Session {
   return sessionFromTable(fb.Session.getRootAsSession(new ByteBuffer(buf)));
 }
 
+// encodeWalletBuy wraps the product id for a chip spend (POST /user/wallet/buy).
+export function encodeWalletBuy(productId: string): Uint8Array {
+  const b = new Builder(64);
+  const pid = b.createString(productId);
+  fb.WalletBuyRequest.startWalletBuyRequest(b);
+  fb.WalletBuyRequest.addProductId(b, pid);
+  return finish(b, fb.WalletBuyRequest.endWalletBuyRequest(b));
+}
+
+// decodeWallet reads the wallet payload: the context-visible chip segments and the
+// context-applicable benefits.
+export function decodeWallet(buf: Uint8Array): Wallet {
+  const w = fb.Wallet.getRootAsWallet(new ByteBuffer(buf));
+  const segments: WalletSegment[] = [];
+  for (let i = 0; i < w.segmentsLength(); i++) {
+    const seg = w.segments(i);
+    if (!seg) continue;
+    segments.push({ source: s(seg.source()), chips: seg.chips(), spendable: seg.spendable() });
+  }
+  return {
+    segments,
+    adsForever: w.adsForever(),
+    adsPaidUntilMs: Number(w.adsPaidUntilMs()),
+    hints: w.hints(),
+  };
+}
+
 export function decodeProfile(buf: Uint8Array): Profile {
   const p = fb.Profile.getRootAsProfile(new ByteBuffer(buf));
   return {