Migrate to jekyll-calconnect-theme gem and redesign contact/footer

[ronaldtse]

Summary

• Migrate site from local theme files to the released jekyll-calconnect-theme ~> 0.3 gem
• Override theme header with active page highlighting
• Redesign contact page: replace plain AsciiDoc table with modern card-based layout
• Redesign footer: tighter brand column + 4-col nav grid with social icons
• Fix hero section gap on homepage
• Lower specificity of body content styles (:where(.body)) so Tailwind utilities override correctly on custom pages
• Remove old Liquid Glass design system SCSS files
• Remove camelCase duplicate resource files in _resources/7things/