赵月辉 / fastgpt-migrated

* feat: implement folder depth management and error handling

- Added new error codes for folder depth limits in CommonErrEnum.
- Introduced folder depth validation logic in the parent folder management.
- Implemented API for fetching subtree maximum folder depth.
- Enhanced folder creation and movement operations to respect maximum folder depth constraints.
- Updated UI components to handle folder depth checks and display appropriate error messages.
- Localized new error messages in English and Chinese.

* refactor: simplify folder depth limit to backend validation

Remove frontend drag pre-check and subtreeDepth API; rename env to
MAX_FOLDER_DEPTH with strict IntSchema validation; keep create-folder
button hiding only.

* perf: limit tip

* chore: remove unrelated folder depth changes

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Co-authored-by: archer <545436317@qq.com>