🧪 test: improve getFileIconColor edge-case handling and add unit tests

[beingniloy]

This PR addresses a testing gap in the getFileIconColor utility by refactoring the function to handle complex and tricky filenames, and adding a comprehensive suite of unit tests.

🎯 What

• Refactored getFileIconColor in src/utils.ts to properly identify file extensions for:
  • Files with multiple dots (e.g. test.spec.js)
  • Case-insensitive extensions (e.g. index.HTML)
  • Dotfiles without an extension (e.g. .gitignore) or with an extension (e.g. .eslintrc.json)
  • No extension files (e.g. LICENSE)
  • Filenames with trailing dots (e.g. filename.)
  • Empty or whitespace-only inputs
• Introduced src/utils.test.ts using Node's native test runner and tsx.
• Configured a new "test" script in package.json.

📊 Coverage

The new tests cover:

• Standard extensions
• Case insensitivity
• Filenames with multiple dots
• Filenames with no extensions
• Complex edge cases (e.g., dotfiles, trailing dots, and empty/whitespace inputs)
• Unknown extensions

✨ Result

We now have reliable, repeatable unit test execution that verifies the robustness of filename-to-color mapping in the editor tree.

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PR created automatically by Jules for task 7433813977281215123 started by @beingniloy

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