feat(cli): scaffold fetch-style edge functions

[jgoux]

Summary

Updates the next CLI Edge Function scaffold to use the Web Fetch-style export default { fetch(...) } authoring model instead of Deno.serve(...).

New functions now get a function-local package.json with no default dependencies, and no generated deno.json. This makes the default template dependency-free while establishing the package-manifest boundary for users who add dependencies under supabase/functions/<function-name> and import them by bare specifier from function code.

Notes

Existing deno.json manifest detection remains in shared config so existing projects and explicit import-map flows keep working.

[github-actions]

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