refactor: replace raw SQL with repository interfaces in entranceserver and API server

Extract all direct database calls from entranceserver (2 calls) and
API server (17 calls) into typed repository interfaces with PostgreSQL
implementations, matching the pattern established in signserver and
channelserver.

Entranceserver: EntranceServerRepo, EntranceSessionRepo
API server: APIUserRepo, APICharacterRepo, APISessionRepo

Also fix the 3 remaining fmt.Sprintf calls inside logger invocations
in handlers_commands.go and handlers_stage.go, replacing them with
structured zap fields.

Unskip 5 TestNewAuthData* tests that previously required a real
database — they now run with mock repos.

server/api/api_server.go

@@ -27,7 +27,9 @@ type APIServer struct {
 	sync.Mutex
 	logger         *zap.Logger
 	erupeConfig    *cfg.Config
-	db             *sqlx.DB
+	userRepo       APIUserRepo
+	charRepo       APICharacterRepo
+	sessionRepo    APISessionRepo
 	httpServer     *http.Server
 	isShuttingDown bool
 }
@@ -37,9 +39,13 @@ func NewAPIServer(config *Config) *APIServer {
 	s := &APIServer{
 		logger:      config.Logger,
 		erupeConfig: config.ErupeConfig,
-		db:          config.DB,
 		httpServer:  &http.Server{},
 	}
+	if config.DB != nil {
+		s.userRepo = NewAPIUserRepository(config.DB)
+		s.charRepo = NewAPICharacterRepository(config.DB)
+		s.sessionRepo = NewAPISessionRepository(config.DB)
+	}
 	return s
 }