feat(ui): wallet storefront redesign — split buy/spend, compact balance, exchange confirm

Reworks the Wallet screen to be more compact and to separate the two flows, and fixes a
reported bug.

Bug: buying a value with too few chips showed the generic "Something went wrong" toast — the
backend's `insufficient_chips` (409) code was propagated correctly but had no i18n mapping, so
`errorKey` fell back to `error.generic`. Add `error.insufficient_chips` / `error.product_not_found`.
Also disable a value's Exchange button up front when the spendable balance cannot cover it (the
server stays authoritative).

Redesign:
- a compact **balance** row leads the screen — the context's own chips (🪙 N) then any linked
  other-platform chips behind that platform's logo (monospaced digits); inside a VK/TG store only
  that store's own segment shows;
- the benefits section is renamed **Active**, moved above the store, shows one inline line
  (hints + ad-free) and hides when nothing is active;
- the **store** splits by a two-way toggle into **Buy chips** (money packs + the watch-an-ad row at
  the top) and **Spend chips** (values, exchanged for chips);
- a value's action reads **Exchange** and opens a single confirmation dialog (chip spends are
  instant, with no provider window to confirm them); the existing cross-platform store-compliance
  warning folds into that same dialog when the spend would draw VK/TG chips.

No payments-model or wire change; the money→chips→values model is unchanged (verified: money buys
only chip packs, values are chips-only — "no-ads for money" is structurally impossible).

Tests: wallet e2e updated for the new layout (chromium + webkit green). Docs: FUNCTIONAL (+_ru)
wallet story rewritten. App bundle budget 126 → 127 KB (always-loaded settings hub).

ui/scripts/bundle-size.mjs

@@ -34,10 +34,11 @@ const DIST = 'dist';
 // Telegram Stars openInvoice / VK order-box launch and the per-button in-flight state ride the same
 // always-loaded Wallet screen, then to 126 for the in-game board-feedback UX — the staged-play
 // highlight geometry (lib/formed.ts), the on-board score badge and the bag / turn-strip / board-zoom
-// wiring live in the always-loaded Game / Board / Rack screens. The heavy parts — the dict loader,
-// the move generator and the preload orchestration — still stay in lazy chunks. Scoped CSS lands in
-// the CSS chunk, not this JS budget.
-const BUDGET = { app: 126, shared: 31, landing: 5 };
+// wiring live in the always-loaded Game / Board / Rack screens, then to 127 for the wallet storefront
+// redesign — its buy/spend toggle, compact balance and exchange-confirm dialog ride the same
+// always-loaded Wallet screen. The heavy parts — the dict loader, the move generator and the preload
+// orchestration — still stay in lazy chunks. Scoped CSS lands in the CSS chunk, not this JS budget.
+const BUDGET = { app: 127, shared: 31, landing: 5 };
 
 // gzipped returns the gzipped byte size of a built asset, or 0 when the reference is not a
 // local file (e.g. the Telegram SDK loaded from a CDN) or is missing.