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.

docs/ARCHITECTURE.md

@@ -262,6 +262,13 @@ Key points:
   check for resign. The engine exposes a
   decoded, solver-free API (`SubmitPlay`/`SubmitExchange`/`EvaluatePlay`/
   `HintView`/`Hand`) so `internal/game` drives it without importing the solver.
+  A play's **orientation (H/V) is inferred from the placed tiles and the board**,
+  not supplied by the caller: two or more tiles fix it by the line they share; a
+  lone tile takes the axis along which it abuts existing tiles (the longer word
+  winning, horizontal on a tie), so a single tile extending an existing word
+  vertically is accepted. Journal replay instead trusts the **stored** direction
+  (`SubmitPlayDir`, §9.1) to reproduce a committed game exactly rather than
+  re-deriving it.
 - The **game domain** (`internal/game`) owns everything the engine does not —
   persistence, turn scheduling, the configurable turn timeout / auto-resign, the
   hint budget, word-check complaints, history and GCG — and is the engine's only
@@ -469,7 +476,8 @@ and — in a per-move JSON payload — the acting player's rack before the move
 `?` for a blank), and for a play its direction, main-word anchor, placed tiles
 (letter as text, coordinate, blank flag) and the words formed; for an exchange,
 the swapped tiles. This is exactly what is needed both to **replay the game
-through the engine** (a cache miss) and to render history or emit GCG **without a
+through the engine** (a cache miss; replay trusts the stored direction rather than
+re-deriving it, so the rebuild matches the committed game) and to render history or emit GCG **without a
 dictionary**: the board for visual replay is reconstructed by applying placements
 onto an empty grid, since moves were validated at play time and scores are
 stored. `variant` and `dict_version` are kept as **metadata only** (audit,

docs/FUNCTIONAL.md

@@ -92,9 +92,12 @@ settings and the game starts once every invitee has accepted — any decline can
 expires after seven days.
 
 ### Playing a game
-Place tiles, pass, exchange, or resign. A play is validated against the game's
-dictionary at submit time and scored; an unlimited preview reports what a
-tentative move would score and whether it is legal. The dictionary check tool is
+Place tiles, pass, exchange, or resign. Tiles are laid without choosing a
+direction — the game infers the play's orientation, so a single tile that extends
+an existing word (down a column or across a row) is accepted. A play is validated
+against the game's dictionary at submit time and scored; an unlimited preview
+reports the word(s) a tentative move would form and its score, or that it is not
+legal, and the move is offered for submission only once it is confirmed legal. The dictionary check tool is
 unlimited and offers a complaint on any result. Hints are governed per game —
 whether they are allowed and how many each player starts with — and draw on a
 personal hint wallet once the per-game allowance is spent. The game ends when the

docs/FUNCTIONAL_ru.md

@@ -96,9 +96,12 @@ nudge) приходят от бота **этой партии** — по язы
 ответа приглашение протухает через семь дней.
 
 ### Игровой процесс
-Выкладывание фишек, пас, обмен или сдача. Ход проверяется по словарю партии при
-сдаче и считается; безлимитный предпросмотр сообщает, сколько принёс бы
-предполагаемый ход и легален ли он. Инструмент проверки слова безлимитный и
+Выкладывание фишек, пас, обмен или сдача. Фишки кладутся без выбора направления —
+игра сама определяет ориентацию хода, поэтому одна фишка, продолжающая уже лежащее
+слово (по столбцу или по строке), принимается. Ход проверяется по словарю партии при
+сдаче и считается; безлимитный предпросмотр показывает слово (или слова), которое
+образует предполагаемый ход, и его очки — либо что ход недопустим, — и ход можно
+отправить только после подтверждения, что он допустим. Инструмент проверки слова безлимитный и
 предлагает пожаловаться на любой результат. Подсказки управляются настройками
 партии — разрешены ли они и сколько их у каждого игрока на старте — и расходуют
 личный кошелёк подсказок после исчерпания внутриигрового лимита. Партия