feat(site): redesign homepage as a developer terminal with live JSON playground

Single-page developer-tool design (Space Grotesk + JetBrains Mono, mint accent, 1px borders). Fetches the static v1/ dump live: hero terminal cycling real requests, interactive playground, featured device cards with conic score rings, endpoint list and coverage stats shown as scored/total.

Theme follows the OS prefers-color-scheme until the user toggles (persisted in localStorage, applied pre-paint to avoid a flash). Replaces the previous homepage.

Author: Seungpyo1007