docs: tighten README runtimes section and adapter framing

[tomaspozo]

Summary

• Add Vercel Functions to the Runtimes section (partner ask) and reshape the section into a 5-row table covering only deployment targets — no more mixing platforms, JS runtimes, and frameworks in one list.
• Trim the Framework Adapters section: drop the inline Hono / H3 code examples (already in docs/adapters/*.md) and rewrite the intro to clearly frame adapters as a community initiative, with a single pointer to src/adapters/README.md for contribution requirements.
• Repoint the now-orphan #hono / #h3--nuxt anchors to #framework-adapters.

[pkg-pr-new]

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npm i https://pkg.pr.new/@supabase/server@68

commit: 3556319