fix(jsr): resolve slow-type errors in elysia and h3 adapters

[tomaspozo]

Summary

• Adds explicit return type to the Elysia withSupabase plugin and exports SupabaseError so it's reachable from the public API (JSR missing-explicit-return-type).
• Removes the declare module 'h3' ambient augmentation from src/adapters/h3/middleware.ts (JSR unsupported-ambient-module); the middleware now casts event.context locally. The augmentation moved into the test file (JSR-excluded) and the H3 docs gained a one-time snippet users add in their own project for typed event.context.supabaseContext.

[pkg-pr-new]

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npm i https://pkg.pr.new/@supabase/server@69

commit: 9cdc788