CSS theme cleanup: Replace duplicate light/dark palette methods with one theme config.

[Gitjay11]

Description

This PR fixes Theme CSS Cleanup #2170

palettes.ts used to have two separate methods, [setColorsLight] and [setColorsDark] , that did the same thing with a long list of repeated style.setProperty(...) calls. That meant the same CSS variable names were written twice which made it easy to accidentally update one theme and forget the other. This change moves all theme variables into one configuration object that stores both the light and dark values, and a single helper applies the correct set depending on the theme. As a result, the light and dark themes stay consistent, the code is shorter and adding or changing a theme variable only needs to be done in one place.

Testing

• Switched to Mito Light and verified colors apply correctly
• Switched to Mito Dark and verified colors apply correctly
• Toggled mito Light/Dark multiple times in the same session

Documentation

No documentation changes required.

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