Configurable footer background and title colors

[paulojunior-ufla]

Summary

• Add footer background color setting (colour picker) with cache reset on change.
• Add footer title color setting (colour picker) with cache reset on change.
• Apply $footerbgcolor to .footer-main with a $night_rider fallback via !default.
• Apply $footertitlecolor to h2 elements within .footer-main with a $secondary fallback via !default.

Motivation

• Allow administrators to control the footer background color without editing SCSS.
• Allow administrators to control the footer title color without editing SCSS.
• Keep clear SCSS fallbacks aligned with the theme's defaults.
• Provide flexible customization while maintaining visual consistency with the theme's color palette.