Add Gantheory theme

[tracy-codes]

Summary

• Adds Gantheory dark theme for Zed
• Ported from the VSCode Gantheory theme by shunyaoshih

Features

• Very dark background (#040404) for reduced eye strain
• Vibrant syntax highlighting with cyan keywords, bright cyan functions, orange strings, purple numbers, pink punctuation
• Full terminal ANSI color support
• Git status colors

Links

• Extension repo: https://github.com/tracy-codes/zed-gantheory-theme
• Original VSCode theme: https://github.com/shunyaoshih/vscode-theme-gantheory

[cla-bot]

We require contributors to sign our Contributor License Agreement, and we don't have @tracy-codes on file. You can sign our CLA at https://zed.dev/cla. Once you've signed, post a comment here that says '@cla-bot check'.

[tracy-codes]

We require contributors to sign our Contributor License Agreement, and we don't have @tracy-codes on file. You can sign our CLA at https://zed.dev/cla. Once you've signed, post a comment here that says '@cla-bot check'.

@cla-bot check

[cla-bot]

The cla-bot has been summoned, and re-checked this pull request!