feat(stats): show the best move word per game variant

Replace the single "best move" number on the statistics screen with a
full-width per-variant breakdown: the highest-scoring play in each variant
the player has played, drawn as game tiles (a wildcard shows its letter but
no value), with the words and scores right-aligned to shared edges.

- backend: new account_best_move table (PK account_id+variant) keeping the
  main word as JSON tiles {letter,value,blank}; captured at game finish in
  buildStats (blank flags taken from every placed blank — equivalent to the
  final board), upserted in the finish transaction and replaced only by a
  strictly higher-scoring play. Guest/honest-AI games still record nothing.
  GetStats + statsDTO expose best_moves.
- wire: StatsView gains best_moves:[BestMoveView{variant,score,word:[BestMoveTile]}]
  (trailing, backward-compatible); gateway encodeStats + UI codec updated.
- ui: new WordTiles component (board's tile look, fixed px size); Stats.svelte
  drops the maxWord card and adds the full-width best-move card (catalogue
  order, empty variants omitted).
- docs: ARCHITECTURE §9 + schema, FUNCTIONAL (+ru), UI_DESIGN.

Tests: mainWordTiles unit + buildStats end-to-end (inttest) + gateway and UI
codec round-trips (incl. a blank tile) + e2e.

backend/internal/postgres/jet/backend/model/account_best_move.go

@@ -0,0 +1,21 @@
+//
+// Code generated by go-jet DO NOT EDIT.
+//
+// WARNING: Changes to this file may cause incorrect behavior
+// and will be lost if the code is regenerated
+//
+
+package model
+
+import (
+	"github.com/google/uuid"
+	"time"
+)
+
+type AccountBestMove struct {
+	AccountID uuid.UUID `sql:"primary_key"`
+	Variant   string    `sql:"primary_key"`
+	Score     int32
+	Tiles     string
+	UpdatedAt time.Time
+}

backend/internal/postgres/jet/backend/table/account_best_move.go

@@ -0,0 +1,90 @@
+//
+// Code generated by go-jet DO NOT EDIT.
+//
+// WARNING: Changes to this file may cause incorrect behavior
+// and will be lost if the code is regenerated
+//
+
+package table
+
+import (
+	"github.com/go-jet/jet/v2/postgres"
+)
+
+var AccountBestMove = newAccountBestMoveTable("backend", "account_best_move", "")
+
+type accountBestMoveTable struct {
+	postgres.Table
+
+	// Columns
+	AccountID postgres.ColumnString
+	Variant   postgres.ColumnString
+	Score     postgres.ColumnInteger
+	Tiles     postgres.ColumnString
+	UpdatedAt postgres.ColumnTimestampz
+
+	AllColumns     postgres.ColumnList
+	MutableColumns postgres.ColumnList
+	DefaultColumns postgres.ColumnList
+}
+
+type AccountBestMoveTable struct {
+	accountBestMoveTable
+
+	EXCLUDED accountBestMoveTable
+}
+
+// AS creates new AccountBestMoveTable with assigned alias
+func (a AccountBestMoveTable) AS(alias string) *AccountBestMoveTable {
+	return newAccountBestMoveTable(a.SchemaName(), a.TableName(), alias)
+}
+
+// Schema creates new AccountBestMoveTable with assigned schema name
+func (a AccountBestMoveTable) FromSchema(schemaName string) *AccountBestMoveTable {
+	return newAccountBestMoveTable(schemaName, a.TableName(), a.Alias())
+}
+
+// WithPrefix creates new AccountBestMoveTable with assigned table prefix
+func (a AccountBestMoveTable) WithPrefix(prefix string) *AccountBestMoveTable {
+	return newAccountBestMoveTable(a.SchemaName(), prefix+a.TableName(), a.TableName())
+}
+
+// WithSuffix creates new AccountBestMoveTable with assigned table suffix
+func (a AccountBestMoveTable) WithSuffix(suffix string) *AccountBestMoveTable {
+	return newAccountBestMoveTable(a.SchemaName(), a.TableName()+suffix, a.TableName())
+}
+
+func newAccountBestMoveTable(schemaName, tableName, alias string) *AccountBestMoveTable {
+	return &AccountBestMoveTable{
+		accountBestMoveTable: newAccountBestMoveTableImpl(schemaName, tableName, alias),
+		EXCLUDED:             newAccountBestMoveTableImpl("", "excluded", ""),
+	}
+}
+
+func newAccountBestMoveTableImpl(schemaName, tableName, alias string) accountBestMoveTable {
+	var (
+		AccountIDColumn = postgres.StringColumn("account_id")
+		VariantColumn   = postgres.StringColumn("variant")
+		ScoreColumn     = postgres.IntegerColumn("score")
+		TilesColumn     = postgres.StringColumn("tiles")
+		UpdatedAtColumn = postgres.TimestampzColumn("updated_at")
+		allColumns      = postgres.ColumnList{AccountIDColumn, VariantColumn, ScoreColumn, TilesColumn, UpdatedAtColumn}
+		mutableColumns  = postgres.ColumnList{ScoreColumn, TilesColumn, UpdatedAtColumn}
+		defaultColumns  = postgres.ColumnList{UpdatedAtColumn}
+	)
+
+	return accountBestMoveTable{
+		Table: postgres.NewTable(schemaName, tableName, alias, allColumns...),
+
+		//Columns
+		AccountID: AccountIDColumn,
+		Variant:   VariantColumn,
+		Score:     ScoreColumn,
+		Tiles:     TilesColumn,
+		UpdatedAt: UpdatedAtColumn,
+
+		AllColumns:     allColumns,
+		MutableColumns: mutableColumns,
+		DefaultColumns: defaultColumns,
+	}
+}

backend/internal/postgres/migrations/00009_best_move.sql

@@ -0,0 +1,25 @@
+-- +goose Up
+-- Per-account, per-variant best single move: the highest-scoring play the account has
+-- ever made in each game variant. It exists so the statistics screen can show the word
+-- itself broken down by variant, not just the dimensionless aggregate
+-- account_stats.max_word_points. tiles is the move's main word as an ordered JSON array of
+-- {letter, value, blank} objects (value 0 and blank true for a wildcard), so the client
+-- renders it as game tiles without needing the variant's alphabet table. score is the
+-- play's total points (every word it formed plus the all-tiles bonus), matching
+-- max_word_points. A row is replaced only by a strictly higher-scoring play. It is written
+-- at game finish alongside account_stats; guest and honest-AI games never record statistics,
+-- so they never write here. See docs/ARCHITECTURE.md §9.
+SET search_path = backend, pg_catalog;
+
+CREATE TABLE account_best_move (
+    account_id uuid        NOT NULL REFERENCES accounts (account_id) ON DELETE CASCADE,
+    variant    text        NOT NULL,
+    score      integer     NOT NULL,
+    tiles      jsonb       NOT NULL,
+    updated_at timestamptz NOT NULL DEFAULT now(),
+    PRIMARY KEY (account_id, variant)
+);
+
+-- +goose Down
+SET search_path = backend, pg_catalog;
+DROP TABLE IF EXISTS account_best_move;