Closes 155 - Fix FolderService to prevent deleting root user directory, and bypassing the trash

[vanxa]

Summary

• Create a util class, FileUtil, and refactor path validation and resolution (was duplicated across two classes)
• Change FolderService#deleteFolder to call TrashService#moveToTrash
• Add a check to prevent FolderService from deleting the entire user root directory
• Add FileUtil tests

Still a DRAFT. TODO:

• Add tests to the FolderService deleteFolder()
• Check if code can reuse TrashService#moveToTrash recursively (merge FolderService#deleteFolder with TrashService#moveToTrash)

Linked issue

Closes #155

[vanxa]

It should be noted, currently this produces a circular dependency between the TrashService and the FolderService, so it may not compile. Will review and rework.

[github-actions]

Agent review

Two blocking problems in FolderService.deleteFolder: a circular bean dependency with TrashService (app won't start) and a trash call that can't work on directories or per-entry paths. Existing tests also still use the old signature. See inline comments.

Generated by Pull Request Review for #158 · copilot · auto · 21.6 AIC · ⌖ 5.07 AIC · ⊞ 7K

[github-actions]

Circular dependency: TrashService is @RequiredArgsConstructor with a FolderService folderService field (and calls folderService.validatePath). Injecting TrashService into FolderService via constructor creates a cycle, so the Spring context fails to start (BeanCurrentlyInCreationException). The FolderService used to have no dependencies. Move the validation into FileUtil and have TrashService use it, or otherwise break the cycle.

[github-actions]

Wrong behaviour: this runs inside a per-path Files.walk(folder) loop but always passes relativeFolderPath (the folder, not p). TrashService.moveToTrash throws ResourceNotFoundException unless the source is a regular file, so deleting any folder fails on the first iteration (folder is not a regular file). Even if it worked, a folder with N entries would trigger N calls on the same path. Trash each regular file under its own relative path (rootPath.relativize(p)), then delete the remaining empty directories. The existing deleteFolder_* tests in FolderServiceTest still call the old 2-arg signature (compile error) and nothing covers the new behaviour, the root-folder check, or the trash move.