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.

pkg/fbs/scrabble.fbs

@@ -458,14 +458,35 @@ table LinkResult {
   session:Session;
 }
 
+// BestMoveTile is one letter cell of a best-move word: its concrete letter (the designated
+// letter for a blank), its tile point value (0 for a blank) and whether it is a blank. It
+// lets the client render the word as game tiles without the variant's alphabet table.
+table BestMoveTile {
+  letter:string;
+  value:int;
+  blank:bool;
+}
+
+// BestMoveView is an account's highest-scoring single play within one game variant: the
+// variant label, the play's total score (matching max_word_points for that variant) and its
+// main word as ordered tiles.
+table BestMoveView {
+  variant:string;
+  score:int;
+  word:[BestMoveTile];
+}
+
 // StatsView is a durable account's lifetime statistics (games-played and win-rate
-// are derived client-side).
+// are derived client-side). best_moves breaks the best move down per variant, carrying the
+// word itself; it is empty for an account with no recorded play and lists only variants the
+// account has played (added trailing — backward-compatible).
 table StatsView {
   wins:int;
   losses:int;
   draws:int;
   max_game_points:int;
   max_word_points:int;
+  best_moves:[BestMoveView];
 }
 
 // TargetRequest names a single counterpart account (friend request/cancel/unfriend,

pkg/fbs/scrabblefb/BestMoveTile.go

@@ -0,0 +1,90 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package scrabblefb
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type BestMoveTile struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsBestMoveTile(buf []byte, offset flatbuffers.UOffsetT) *BestMoveTile {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &BestMoveTile{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func FinishBestMoveTileBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.Finish(offset)
+}
+
+func GetSizePrefixedRootAsBestMoveTile(buf []byte, offset flatbuffers.UOffsetT) *BestMoveTile {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &BestMoveTile{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func FinishSizePrefixedBestMoveTileBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.FinishSizePrefixed(offset)
+}
+
+func (rcv *BestMoveTile) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *BestMoveTile) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *BestMoveTile) Letter() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *BestMoveTile) Value() int32 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.GetInt32(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *BestMoveTile) MutateValue(n int32) bool {
+	return rcv._tab.MutateInt32Slot(6, n)
+}
+
+func (rcv *BestMoveTile) Blank() bool {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(8))
+	if o != 0 {
+		return rcv._tab.GetBool(o + rcv._tab.Pos)
+	}
+	return false
+}
+
+func (rcv *BestMoveTile) MutateBlank(n bool) bool {
+	return rcv._tab.MutateBoolSlot(8, n)
+}
+
+func BestMoveTileStart(builder *flatbuffers.Builder) {
+	builder.StartObject(3)
+}
+func BestMoveTileAddLetter(builder *flatbuffers.Builder, letter flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(letter), 0)
+}
+func BestMoveTileAddValue(builder *flatbuffers.Builder, value int32) {
+	builder.PrependInt32Slot(1, value, 0)
+}
+func BestMoveTileAddBlank(builder *flatbuffers.Builder, blank bool) {
+	builder.PrependBoolSlot(2, blank, false)
+}
+func BestMoveTileEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}

pkg/fbs/scrabblefb/BestMoveView.go

@@ -0,0 +1,101 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package scrabblefb
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type BestMoveView struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsBestMoveView(buf []byte, offset flatbuffers.UOffsetT) *BestMoveView {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &BestMoveView{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func FinishBestMoveViewBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.Finish(offset)
+}
+
+func GetSizePrefixedRootAsBestMoveView(buf []byte, offset flatbuffers.UOffsetT) *BestMoveView {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &BestMoveView{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func FinishSizePrefixedBestMoveViewBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.FinishSizePrefixed(offset)
+}
+
+func (rcv *BestMoveView) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *BestMoveView) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *BestMoveView) Variant() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *BestMoveView) Score() int32 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.GetInt32(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *BestMoveView) MutateScore(n int32) bool {
+	return rcv._tab.MutateInt32Slot(6, n)
+}
+
+func (rcv *BestMoveView) Word(obj *BestMoveTile, j int) bool {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(8))
+	if o != 0 {
+		x := rcv._tab.Vector(o)
+		x += flatbuffers.UOffsetT(j) * 4
+		x = rcv._tab.Indirect(x)
+		obj.Init(rcv._tab.Bytes, x)
+		return true
+	}
+	return false
+}
+
+func (rcv *BestMoveView) WordLength() int {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(8))
+	if o != 0 {
+		return rcv._tab.VectorLen(o)
+	}
+	return 0
+}
+
+func BestMoveViewStart(builder *flatbuffers.Builder) {
+	builder.StartObject(3)
+}
+func BestMoveViewAddVariant(builder *flatbuffers.Builder, variant flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(variant), 0)
+}
+func BestMoveViewAddScore(builder *flatbuffers.Builder, score int32) {
+	builder.PrependInt32Slot(1, score, 0)
+}
+func BestMoveViewAddWord(builder *flatbuffers.Builder, word flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(2, flatbuffers.UOffsetT(word), 0)
+}
+func BestMoveViewStartWordVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT {
+	return builder.StartVector(4, numElems, 4)
+}
+func BestMoveViewEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}

pkg/fbs/scrabblefb/StatsView.go

@@ -101,8 +101,28 @@ func (rcv *StatsView) MutateMaxWordPoints(n int32) bool {
 	return rcv._tab.MutateInt32Slot(12, n)
 }
 
+func (rcv *StatsView) BestMoves(obj *BestMoveView, j int) bool {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(14))
+	if o != 0 {
+		x := rcv._tab.Vector(o)
+		x += flatbuffers.UOffsetT(j) * 4
+		x = rcv._tab.Indirect(x)
+		obj.Init(rcv._tab.Bytes, x)
+		return true
+	}
+	return false
+}
+
+func (rcv *StatsView) BestMovesLength() int {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(14))
+	if o != 0 {
+		return rcv._tab.VectorLen(o)
+	}
+	return 0
+}
+
 func StatsViewStart(builder *flatbuffers.Builder) {
-	builder.StartObject(5)
+	builder.StartObject(6)
 }
 func StatsViewAddWins(builder *flatbuffers.Builder, wins int32) {
 	builder.PrependInt32Slot(0, wins, 0)
@@ -119,6 +139,12 @@ func StatsViewAddMaxGamePoints(builder *flatbuffers.Builder, maxGamePoints int32
 func StatsViewAddMaxWordPoints(builder *flatbuffers.Builder, maxWordPoints int32) {
 	builder.PrependInt32Slot(4, maxWordPoints, 0)
 }
+func StatsViewAddBestMoves(builder *flatbuffers.Builder, bestMoves flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(5, flatbuffers.UOffsetT(bestMoves), 0)
+}
+func StatsViewStartBestMovesVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT {
+	return builder.StartVector(4, numElems, 4)
+}
 func StatsViewEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }