Native <input type="checkbox"> elements were invisible in production
because @tailwindcss/forms is not installed. UCheckbox renders properly
with the Nuxt UI theme.
Standardizes color values and styling using the new tokens:
- Replaces hardcoded colors with semantic variables
- Updates background/text/border classes for light/dark mode
- Migrates inputs to UInput/USelect/UTextarea components
- Removes redundant style declarations
