refactor: simplify casbin version handling with environment variables

[HashCookie]

Description

This PR simplifies the way of handling Casbin versions in the editor:

• Removing the webpack plugin approach that generates a JSON file
• Using Next.js environment variables to inject the version at build time
• Cleaning up related files and code

Benefits

• Simpler code structure
• No extra network requests
• No file I/O during build

Testing

• Casbin version still displays correctly
• Build process works without errors

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[hsluoyz]

🎉 This PR is included in version 1.27.0 🎉

The release is available on GitHub release

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