[docs] Provide a complete theme variable reference

## Describe the feature request

The current documentation includes a **Colors** section that explains semantic color tokens and shows their resolved values for light and dark mode. While this is helpful, it is **not sufficient as a full theme reference**.

What’s missing is a **centralized, style reference** that lists *all* theme variables exposed by Kumo UI in a way that is easy to browse, copy, and reuse, similar to Tailwind’s default theme variable reference:

https://tailwindcss.com/docs/theme#default-theme-variable-reference

This would help developers who want to:
- Copy tokens directly into their own Tailwind config
- Understand the full design token surface area
- Avoid importing Kumo’s Tailwind styles when they prefer explicit configuration

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## Current behavior

- Docs provide:
- A detailed **Colors** section focused on semantic color tokens
- Guidance on light/dark mode, themes, and token usage
- However:
- The documentation is scoped mainly to colors
- There is no single page that lists **all theme variables** in one place
- Tokens are not presented in a compact, reference-style format
- Developers must inspect source files or generated CSS to discover the full set of tokens

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## Expected behavior

- Add a **dedicated theme variable reference page** that:
- Lists all available theme tokens (not only colors)
- Presents them in a copy-friendly, tabular or grouped format
- Clearly shows token names and their resolved values
- The structure and intent should mirror Tailwind’s own theme reference:
https://tailwindcss.com/docs/theme#default-theme-variable-reference
- This reference should complement (not replace) the existing semantic color guidance

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## Environment and versions

- **Kumo version:** v1.0.0
- **Docs section:** Colors, https://kumo-ui.com/colors/
- **Reference example:**
https://tailwindcss.com/docs/theme#default-theme-variable-reference