feat: make direct imports production-safe

[birkskyum]

Summary

• export the real browser and SSR implementations under the development condition
• export a children-only no-op implementation by default
• register server-function observers from the browser entry
• expose matching types from every entry

Why

Apps with custom server and client entries should be able to import DevToolbar directly without shipping devtools code in production. This moves the environment boundary into the package and lets solid-vite-plugin#317 remove its public virtual devtools module.

Test

• pnpm build
• pnpm test
• pnpm check
• solid-vite-plugin Start dev suite (63/63)
• solid-vite-plugin custom entry suite (20/20)