Add SolidStart SSR example for Supabase SSR (auth) client

# Improve documentation ## Link https://supabase.com/docs/guides/auth/server-side/creating-a-client ## Describe the problem Hi Supabase team! I noticed the current [SSR auth docs](https://supabase.com/docs/guides/auth/server-side/creating-a-client) include examples for Next.js, Astro, SvelteKit, and Hono, but there isn't one for SolidStart. Since SolidStart is an SSR-first framework supporting middleware, I thought I'd raise this as a potential enhancement. I noticed some confusion regarding this subject in [this GitHub discussion.](https://github.com/orgs/supabase/discussions/12891) ## Describe the improvement Some confusion exists around the actual implementation using SolidStart and the Supabase SSR client. - Unlike Next.js, SolidStart doesn't have the same `NextRequest`/`NextResponse` API, so creating a Supabase server client requires slightly different handling of cookies and session refreshes. - Having an example would reduce confusion around misusing "use server" (which cannot be used in combination with the middleware) or exposing server clients to the client bundle. ## Additional context I've implemented a working SolidStart SSR example with: - Middleware for session sync + redirect on initial load - Loader-level auth enforcement in server routes - Safe server-side Supabase client creation I'd be happy to contribute this example and draft docs if this is something you'd consider adding. Thanks for considering!