feat: Add dark/light theme toggle to Landing Page

[ish1416]

• Add ThemeContext for theme state management with localStorage persistence
• Add ThemeToggle component with sun/moon icons
• Update Navbar with theme toggle and dynamic logo switching
• Add comprehensive dark mode classes throughout Landing Page
• Enhance logo visibility with glassmorphism (Warp) and brightness filters (DB logos)
• Maintain existing animations and layout structure
• Support system preference detection (prefers-color-scheme)
• Ensure WCAG AAA contrast compliance in both themes

Fixes: Landing Page theme toggle implementation

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[ish1416]

[ish1416]

@1ilit Can you review this PR?

[1ilit]

out of scope