refactor: remove legacy .lpschem format (TODO 117)

- Delete schematic/legacy/lpschem/ (LPSchematicLegacy + 5 pojo Gson models)
- Delete schematic/convert/LpschemConverter and /lp schematic convert command
- Remove SchematicClipboardBuilder.fromLegacy, convert branches in dispatcher/
  tab-completer/help, locales (ru/en), SCHEMATICS.md and yml comments
- Kept only .schem (WorldEdit) + .nbt
- Build green: checkstyle 0 errors, PMD 33

src/main/resources/locales/ru.yml

@@ -353,7 +353,6 @@ schematic:
     line_pos2: "&#FF4444/LoParkour schematic pos2 &#404040- &#A0A0A0Позиция 2"
     line_create: "&#FF4444/LoParkour create <сложность> &#404040- &#A0A0A0Сохранить в .schem + yml"
     line_create_named: "&#FF4444/LoParkour schematic create <имя> <сложность> &#404040- &#A0A0A0С именем"
-    line_convert: "&#FF4444/LoParkour schematic convert &#404040- &#A0A0A0.lpschem → .schem"
     line_paste: "&#FF4444/LoParkour schematic paste <имя> &#404040- &#A0A0A0Тестовая вставка"
     line_list: "&#FF4444/LoParkour schematic list &#404040- &#A0A0A0Список"
     line_reload: "&#FF4444/LoParkour schematic reload &#404040- &#A0A0A0Перезагрузка"
@@ -369,8 +368,6 @@ schematic:
   selection_incomplete: "&#FF4444Сначала выделите область (палочка или pos1/pos2)."
   created: "&#A0A0A0Добавлено &#FF4444%s &#404040(сложн. %s) → &#FF4444%s"
   create_failed: "&#FF4444Ошибка: %s"
-  convert_done: "&#A0A0A0Конвертировано: %s, ошибок: %s."
-  convert_truncated: "&#A0A0A0...ещё %s (см. консоль)."
   not_found: "&#FF4444Схема '%s' не найдена."
   pasted: "&#A0A0A0Вставлено: &#FF4444%s&#A0A0A0."