Fix missing Content-Encoding: gzip header for .gz files

[terreng]

Fixes #219

This PR was made by GitHub Copilot AI.

Add logic to handle .gz files and set Content-Encoding: gzip if the remaining string has a valid file extension.

• Modify renderFileContents method in WSC/handlers.js to check if the file has a .gz extension.
• Remove the .gz extension and check if the remaining string has a valid file extension.
• Set the appropriate Content-Type and Content-Encoding headers if the remaining string has a valid file extension.

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[terreng]

It didn't work and I don't know if it worked properly with the existing pre-compression option. It's hard for me to test this.