feat: Auto Context and Dark Mode improvements

[UddipanGamer]

Implements Auto Context feature with token-based optimization and improves Dark Mode consistency across the app.

[Fanzzzd]

Hi @UddipanGamer, thanks so much for this contribution! 🎉

I have a few suggestions:

1. Separate the styling changes into a different PR

It would be great to split the Dark Mode styling improvements into a separate PR so we can review and iterate on each feature independently.

I'm actually considering moving the app's overall design toward a more minimal aesthetic — something closer to Cursor or Linear (clean, dark/light, simple). Your Dark Mode improvements could be a great starting point for that!

If you're interested, I'd suggest:

• Using CSS variables for the color palette (similar to how shadcn/ui handles theming) — this makes it much easier to maintain and switch themes
• Opening a new PR focused purely on styling

2. Auto Context feature

I've tested the Auto Context feature and it works well on my end! I've made a few additional improvements on top of your work:

• Added support for multiple providers (LM Studio, Ollama, OpenAI, Anthropic, OpenRouter)
• Stored the API key securely in the system keychain instead of plain text

btw I'm a bit busy next week. Please feel free to update this PR yourself based on the feedback above if you have time — otherwise, no worries! I can continue the work when I'm back, and I'll make sure your contributions are properly credited.

Thanks again for your work on this! 🙏