- index.css: add :root.light overrides for the sky-* accent used only by the
Caddy settings card (buttons, badges, hovers) + the missing red-950/30 hover
- favicon: add public/favicon.svg (GhostGrid logo) and link it in index.html
- ARCHITECTURE.md: GET /caddy/routes returns a plain array, document the Caddy
startup import, https:// upstream, favicon/public dir, and the SPA-catch-all-last
+ Cache-Control: no-store invariant
