[FEATURE] Support user scripts (Greasemonkey-style) for lightweight features

[harlley]

Is your feature request related to a problem? Please describe.
I often want to experiment with small JavaScript/HTML/CSS snippets that integrate AI-related functionality (for example, using navigator.llm.response). Right now, the only practical way to achieve this is by creating a full Chrome extension, which feels excessive and time-consuming for small and lightweight ideas. This makes it harder to quickly prototype and test simple features.

Describe the solution you'd like
I would like the extension to support loading and running small custom snippets of JavaScript/HTML/CSS directly, similar to how the classic Greasemonkey/Tampermonkey approach works. This would make it much easier to add lightweight AI-related features or experiments without packaging and publishing a full extension. Ideally, snippets could be managed from within the extension interface itself.

Describe alternatives you've considered

• Manually creating a Chrome extension for each small feature, but this requires setup overhead (manifest files, packaging, permissions).
• Using user scripts with Greasemonkey/Tampermonkey, which works for web experiments but doesn’t directly let me use navigator.llm.response and other extension-specific APIs.

Additional context
This feature would allow developers and power users to extend functionality quickly and iterate on ideas much faster. My main interest came from discovering navigator.llm.response, which I think has huge potential for integration into simple UI tweaks, but right now the barrier to entry (building my own extension) makes it less accessible.