Remove redundant loader installer path input in editor

Path is set by the loader upload form below, so the manual
text input was redundant. Drop the field from the editor UI
and stop overwriting the saved value on form submit so an
uploaded loader keeps its path.

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

views/op/editor.ejs

@@ -62,10 +62,6 @@
             <span>로더 버전</span>
             <input name="loaderVersion" value="<%= pack.loaderVersion ?? '' %>" placeholder="예: 0.16.14 / 47.3.0 / 21.4.111-beta" />
           </label>
-          <label class="fullSpan">
-            <span>로더 설치파일 경로</span>
-            <input name="loaderInstallerPath" value="<%= pack.loaderInstallerPath ?? '' %>" placeholder="예: uploads/sample-pack/loaders/..." />
-          </label>
           <label>
             <span>packPath</span>
             <input name="packPath" value="<%= pack.packPath %>" required />