installer: wipe mods/ before install and rename extracted map to pack name

Two follow-ups requested by the user (and the first flagged by the
reviewer for omission):

1) Different Minecraft versions or different packs leave behind mod jars
   that crash Fabric on load. `downloadModsFolder` now removes the entire
   `.mc_custom/mods/` directory before every install — including when the
   pack is vanilla (no modsFolder) so leftovers from a previous modded
   pack get cleared too.

2) `downloadMapZip` renames the single extracted top-level folder to the
   pack name (sanitized for Windows: forbidden chars `<>:"/\|?*` and
   control chars → `_`, trailing space/dot trimmed, reserved names like
   CON/NUL prefixed, empty fallback to `map`). Collisions with user
   worlds get `_2`, `_3` … suffixes so we never overwrite the user's
   own worlds. The marker file tracks the post-rename folder so future
   participant cleanup still removes only what the installer created.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

locales/installer/ko-kr.json

@@ -192,6 +192,9 @@
     "skipServerZip": "서버 파일(serverPath)이 비어 있어 서버 zip 다운로드를 건너뜁니다.",
     "skipMapZip": "맵 다운로드를 건너뜁니다 (mapPath 비어 있음 또는 참가자 모드).",
     "cleanupInstallerMap": "이전 설치에서 풀어둔 맵 {{count}}개를 정리합니다.",
+    "mapRenamed": "맵 폴더 이름 변경: {{from}} → {{to}}",
+    "mapRenameFailed": "맵 폴더 이름 변경 실패 ({{from}} → {{to}}): {{message}}",
+    "clearMods": "기존 mods 폴더({{dir}})를 비우고 새로 받습니다.",
     "skipModsFolder": "modsFolder가 비어 있어 모드 다운로드를 건너뜁니다.",
     "modsIndexFetch": "모드 목록 조회: {{url}}",
     "modsFolderEmpty": "/file/mods/{{folder}}/ 안에 .jar 파일이 없습니다.",