Backend infers play direction; UI previews words and gates submit on legality

A single tile that only extended a word perpendicular to the client-declared
direction was rejected: the UI always sent dir=H for one-tile plays (the
dirOverride/Controls toggle was orphaned in the Stage 7 game rework), so placing
"А" above "БАК" to form "АБАК" failed the solver's main-word-length check even
though the word is in the dictionary.

Make the backend infer a play's orientation from the placed tiles and the board
(internal/engine.resolveDirection): two or more tiles by the line they share, a
lone tile by the axis it abuts (longer word wins, horizontal on a tie). Direction
becomes an output, not an input: drop dir from the SubmitPlay/Eval wire requests
and add it to EvalResult. Journal replay keeps trusting the stored "H"/"V"
(SubmitPlayDir) so a rebuilt game matches the one committed.

UI: stop computing/sending direction; the preview now shows the words a move
forms with its total score (game.previewWords); the make-move control is disabled
until the play is confirmed legal; the "your turn" label hides while tiles are
pending. Delete the orphaned Controls.svelte.

Regenerate the FlatBuffers bindings (Go + TS) and update the gateway transcode
and the loadtest edge client to the new contract. Bake the decision into
ARCHITECTURE.md (§5/§9.1), FUNCTIONAL.md (+ _ru) and the backend README.

ui/src/game/Game.svelte

@@ -12,7 +12,7 @@
   import { connection } from '../lib/connection.svelte';
   import { GatewayError } from '../lib/client';
   import { t, type MessageKey } from '../lib/i18n/index.svelte';
-  import type { Direction, EvalResult, MoveRecord, MoveResult, StateView, Tile } from '../lib/model';
+  import type { EvalResult, MoveRecord, MoveResult, StateView, Tile } from '../lib/model';
   import { lastMoveCells, replay } from '../lib/board';
   import { historyGrid } from '../lib/history';
   import { centre, premiumGrid } from '../lib/premiums';
@@ -42,7 +42,6 @@
   let moves = $state<MoveRecord[]>([]);
   let placement = $state<Placement>(newPlacement([]));
   let preview = $state<EvalResult | null>(null);
-  let dirOverride = $state<Direction | undefined>(undefined);
   let busy = $state(false);
   let zoomed = $state(false);
   let selected = $state<number | null>(null);
@@ -130,7 +129,6 @@
       moves = hist.moves;
       setCachedGame(id, st, hist.moves);
       selected = null;
-      dirOverride = undefined;
       await applyDraft(st);
       recompute();
       refreshRecent();
@@ -491,11 +489,11 @@
     if (previewTimer) clearTimeout(previewTimer);
     // Off-turn the composition is position-only: no score preview or evaluate.
     if (!isMyTurn) return;
-    const sub = toSubmit(placement, dirOverride);
+    const sub = toSubmit(placement);
     if (!sub) return;
     previewTimer = setTimeout(async () => {
       try {
-        preview = await gateway.evaluate(id, sub.dir, sub.tiles, variant);
+        preview = await gateway.evaluate(id, sub.tiles, variant);
       } catch {
         /* best-effort */
       }
@@ -511,17 +509,16 @@
     rackIds = r.rack.map((_, i) => i);
     placement = newPlacement(r.rack);
     selected = null;
-    dirOverride = undefined;
     recompute();
     refreshRecent();
   }
 
   async function commit() {
-    const sub = toSubmit(placement, dirOverride);
+    const sub = toSubmit(placement);
     if (!sub) return;
     busy = true;
     try {
-      applyMoveResult(await gateway.submitPlay(id, sub.dir, sub.tiles, variant));
+      applyMoveResult(await gateway.submitPlay(id, sub.tiles, variant));
       telegramHaptic('success');
       zoomed = false;
     } catch (e) {
@@ -534,7 +531,6 @@
     placement = reset(placement);
     preview = null;
     selected = null;
-    dirOverride = undefined;
     scheduleDraftSave();
   }
 
@@ -857,11 +853,11 @@
       <span>{view.bagLen === 0 ? t('game.bagEmpty') : t('game.bag', { n: view.bagLen })}</span>
       {#if gameOver}
         <strong class="over">{t('game.over')} — {resultText()}</strong>
-      {:else}
+      {:else if placement.pending.length === 0}
         <span class="turn-ind">{isMyTurn ? t('game.yourTurn') : view.game.seats[view.game.toMove]?.displayName ?? ''}</span>
       {/if}
       <span class="scores">
-        {#if preview}{preview.legal ? t('game.scores', { n: preview.score }) : t('game.previewIllegal')}{/if}
+        {#if preview}{preview.legal ? t('game.previewWords', { words: preview.words.join(', '), n: preview.score }) : t('game.previewIllegal')}{/if}
       </span>
     </div>
 
@@ -880,7 +876,7 @@
         />
       </div>
       {#if !gameOver && placement.pending.length > 0}
-        <button class="make" onclick={commit} disabled={busy || !isMyTurn || !connection.online || (preview !== null && !preview.legal)} aria-label={t('game.makeMove')}>✅</button>
+        <button class="make" onclick={commit} disabled={busy || !isMyTurn || !connection.online || !preview?.legal} aria-label={t('game.makeMove')}>✅</button>
       {/if}
     </div>
   {:else}