fix: 修复配额说明重复和undefined问题

- 在editStorageForm中初始化oss_storage_quota_value和oss_quota_unit
- 删除重复的旧配额说明块，保留新的当前配额设置显示

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/node_modules/mkdirp/bin/usage.txt

@@ -0,0 +1,12 @@
+usage: mkdirp [DIR1,DIR2..] {OPTIONS}
+
+  Create each supplied directory including any necessary parent directories that
+  don't yet exist.
+  
+  If the directory already exists, do nothing.
+
+OPTIONS are:
+
+  -m, --mode   If a directory needs to be created, set the mode as an octal
+               permission string.
+