fix Add options "Automatic Directory Creation with Slash" #2640

[asukaminato0721]

fix #2640

New files can use nested paths such as src/components/app.rs; missing directories are created automatically.
Relative . and .. components remain supported.
Absolute, drive-prefixed, and UNC paths are rejected.
~ and $HOME remain literal—no expansion.
Filesystem and permission errors are handled without panics.
Added localized validation messages and regression coverage.

[sinelaw]

This is an autogenerated comment

• Confirms bug: master's perform_file_explorer_rename rejects any / in new-file names, matching issue #2640.
• Fix reuses the existing FileSystem::create_dir_all trait method (no raw std::fs), keeps the pre-existing rename/validation flow, and adds the check only for is_new_file — minimal, non-duplicative, no architectural changes.
• All 14 locale files got the new explorer.new_item_path_must_be_relative key; unit + e2e tests added (fail-without-fix pattern).
• Interactively verified in tmux against a debug build on the PR branch:
  • Ctrl+N → typed src/components/app.rs → dirs auto-created, temp untitled_* file moved into place, buffer focused on the new file.
  • Typed an absolute path (/etc/passwd_evil) → rejected with "New item path must be relative", nothing created outside the project.
  • Typed ../outside_project/evil.txt → allowed and escaped the project dir, matching the issue's explicit spec that ./.. remain literal relative components (not a regression).
• No duplicate/adjacent existing feature found.

---

Generated by Claude Code

[sinelaw]

Escaping the project dir shouldn't be allowed, e.g. we can evaluate the absolute canonical target path and check that its under the project dir