feat(ui): on-device move preview (local eval) with network fallback

Score and validate a tentative move on-device instead of a per-arrangement
network round trip. The dawg reader and the validate/score/direction slice of the
scrabble-solver engine are ported to TypeScript (ui/src/lib/dict), pinned
byte-for-byte to the Go engine by a new `conformance` CI job. The server stays
authoritative — submit_play re-validates — so the local result is an advisory
accelerator only; any cache miss, storage eviction or a bad-connection breaker
falls back to the network evaluate.

- backend: Registry.DictBytes + an authed GET /api/v1/user/dict/{variant}/{version}
  (immutable) streaming the pinned per-game dawg.
- gateway: a session-gated /dict edge route proxying it; fetchDict on the transport.
- client: an IndexedDB blob cache (best-effort, storage.persist()) + a loader
  (memory -> IndexedDB -> network, session-scoped bad-connection breaker) + a lobby
  prefetch (your-turn first); an adapter over the existing premiums/alphabet; a
  DictWarmup overlay while a cold dictionary loads (120ms flash-guard, 5s cap ->
  network); a ?nolocal flag; the DebugPanel reset also clears the dict cache.
- parity: generators backend/cmd/{dictgen,validategen} + gated Vitest suites, run
  in CI against the release dictionaries.
- docs: ARCHITECTURE §5, TESTING, UI_DESIGN, FUNCTIONAL (+ru).

docs/ARCHITECTURE.md

@@ -352,6 +352,17 @@ Key points:
 - History is dictionary-independent (§9.1): the engine emits decoded
   `MoveRecord`s and reconstructs the board from them with `engine.ReplayBoard`
   (alphabet only, no dictionary).
+- The **client mirrors this validation path for an instant move preview** (the
+  local eval, `ui/src/lib/dict`): the dawg reader and the
+  validate/score/direction slice are ported to TypeScript, byte-for-byte against
+  this engine and pinned by the `conformance` CI job. Composing a move is scored
+  on-device with no round trip. It is an **advisory accelerator only** —
+  `submit_play` re-validates on the server, so a wrong or spoofed local result
+  cannot corrupt a game. The pinned per-game dictionary blob is fetched once
+  through a **session-gated `GET /dict/{variant}/{version}`** edge route
+  (immutable; cached in IndexedDB best-effort) and reused across sessions; any
+  miss, storage eviction or a bad-connection breaker falls back to the network
+  `evaluate`. The warm-up overlay is `docs/UI_DESIGN.md`.
 
 ## 6. Game rules