feat(sav): add glassmorphism foundation and UI enhancements

Overview

Implement glassmorphism design system foundation for SAV agent interface with enhanced visual consistency.

Changes

• Enhanced shared UI components with glassmorphism effects (backdrop blur, gradient overlays)
• Updated CustomSelect component with premium visual styling
• Improved FilteringSection with modern glassmorphism cards
• Enhanced ToneStyleSection with consistent design language
• Added smooth transitions and hover effects across components

Technical Details

• All components use ConditionalComponent for conditional rendering
• No commented code
• Consistent color theming through currentColor context
• Responsive design maintained across breakpoints

Components Updated

• custom-select/index.tsx
• filtering-section.tsx
• tone-style-section.tsx
• languages-section.tsx (src/shared/sections/agents/sav/components/languages-section.tsx:1)
• instructions-section.tsx

CLOSE-IAV-601