remove unused theme color background utility classes from background.scss,
swap all instances of bg-theme-color-50 and bg-theme-color-500 with their
corresponding hex values across vue components, and update bg-liner gradient
to use direct hex colors instead of theme variables
Replace all custom `bg-*` utility classes across Vue components with Tailwind's arbitrary hex color notation (e.g. `bg-[#f7f7f7]`). Remove redundant hardcoded background color definitions from src/static/scss/background.scss, clean up template formatting, and update gradient button styles to use direct hex values.
