v0.4.2 — hosted reverse-proxy mode

Hosted mode: run behind Caddy/Nginx at a public origin (--host 0.0.0.0 --port --base-url https://… plus tokens); full guide in docs/hosting.md. Install docs now lead with bunx/npx --stdio. Polish: public-origin startup logs, base-url normalization, honest ask tool description. Verified live on-cluster via Caddy subdomain. Typecheck + 90 vitest tests green.