Return every error as {"error": "..."}

Echo errors, middleware and handlers used three different formats (message object, error object, bare string). One error handler now writes all of them the same way; status codes are unchanged.

internal/server/music_handler.go

@@ -34,7 +34,7 @@ func NewMusicHandler(music *backend.MusicService) *MusicHandler {
 func (m *MusicHandler) GetSong(ctx *echo.Context) error {
 	song, err := strconv.Atoi(ctx.QueryParam("song"))
 	if err != nil {
-		return ctx.String(http.StatusBadRequest, "song must be a number")
+		return echo.NewHTTPError(http.StatusBadRequest, "song must be a number")
 	}
 	path, err := m.music.Song(song)
 	return serveSong(ctx, path, err)
@@ -204,7 +204,7 @@ func (m *MusicHandler) GetAllSoundtracksRandom(ctx *echo.Context) error {
 func (m *MusicHandler) PutPlayed(ctx *echo.Context) error {
 	song, err := strconv.Atoi(ctx.QueryParam("song"))
 	if err != nil {
-		return ctx.JSON(http.StatusBadRequest, err.Error())
+		return echo.NewHTTPError(http.StatusBadRequest, "song must be a number")
 	}
 	logging.GetLogger().Info("Marking song as played", zap.Int("song_id", song))
 	if err := m.music.SetPlayed(ctx.Request().Context(), song); err != nil {