fix(client): show toast notifications on file/folder rename validatio…

[Dakshx07]

Issue:

Fixes #4176

Description:

This PR resolves a usability issue where file and folder rename inputs fail validation silently and revert back to their original names. We now display appropriate toast messages explaining why the rename failed:

• Reverts empty file name -> shows "Please enter a name".
• Reverts empty folder name -> shows "Please enter a name".
• Reverts folder name containing dots/extension -> shows "Folder name cannot contain an extension".
• Reverts file name with missing or unsupported extension -> shows "Invalid file type...".

Changes:

• Refactored validateFileName in FileNode.jsx to check and dispatch showToast notifications on validation failures.
• Updated FileNode.unit.test.jsx to mock showToast and assert that it is called on all validation failures.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.

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