Improve DNS test configuration modals and remove unused theme toggle

[mortezamirkar]

Summary

• migrate the landing page to a Tailwind-based layout with refined hero, results, chart, and footer sections
• overhaul the host and DoH configuration modals with counters, reset buttons, bulk input parsing, inline feedback, and richer server metadata
• add localStorage persistence plus validation helpers, asynchronous DoH capability checks, and remove the abandoned light/dark theme toggle code

Testing

• Manual: opened index.html in a browser, exercised host/DoH modal flows (add, delete, reset, capability check) and ran a DNS benchmark to verify progress + results rendering