Stage 7 (wip): wire remaining ops (backend REST, FBS, gateway transcode) + real UI transport

backend: REST handlers for pass/exchange/resign/hint/evaluate/check_word/complaint/history/chat-list/nudge + new game.ListForAccount (my games) + seat display_name resolution
pkg/fbs: GameActionRequest/ExchangeRequest/EvalRequest/EvalResult/CheckWordRequest/WordCheckResult/ComplaintRequest/HintResult/History/GameList/ChatList + SeatView.display_name; committed Go regenerated (flatc 23.5.26)
gateway: 11 new transcode ops + backendclient methods + FB encoders
ui: edge TS codegen (flatc --ts + protoc-gen-es, committed), FlatBuffers<->model codec, real connect-web transport (binary, bearer auth, Subscribe). prod bundle ~69KB gzip JS

backend/internal/server/dto.go

@@ -66,13 +66,15 @@ type moveRecordDTO struct {
 	Total   int       `json:"total"`
 }
 
-// seatDTO is one seat's public standing.
+// seatDTO is one seat's public standing. DisplayName is resolved from the account
+// store by the handler (the game domain keys seats by account id only).
 type seatDTO struct {
-	Seat      int    `json:"seat"`
-	AccountID string `json:"account_id"`
-	Score     int    `json:"score"`
-	HintsUsed int    `json:"hints_used"`
-	IsWinner  bool   `json:"is_winner"`
+	Seat        int    `json:"seat"`
+	AccountID   string `json:"account_id"`
+	DisplayName string `json:"display_name"`
+	Score       int    `json:"score"`
+	HintsUsed   int    `json:"hints_used"`
+	IsWinner    bool   `json:"is_winner"`
 }
 
 // gameDTO is the shared game summary.