Theme CSS Cleanup

[ngafar]

Bugbot flagged this in mito-ai/src/Extensions/MitoThemes/index.ts:

The MitoPalettes class contains two methods (setColorsLight and setColorsDark) that are structurally identical, each with ~110 lines of repetitive document.documentElement.style.setProperty() calls. This duplicates the list of CSS variable names across both methods, making maintenance error-prone. A data-driven approach using a theme configuration object with variable names as keys and light/dark values would reduce duplication, make it easier to add new variables, and ensure both themes stay in sync.