Handle SvelteKit adapters properly

[endigma]

• with SvelteKit using bun as the package manager and builder does not mean to use bun as the runner
• the runner language is determined by the adapter, not the runtime used to build
• I can use bun to build a nodejs output, and vice versa
• and also: with adapter-static, it should use the nginx thing it does for astro

Stories:

• Right now, if I launch a SvelteKit app that uses bun as its package manager but adapter-node as its runtime, it tries to run the node bundle with bun which won't work properly
• Right now, if I launch a SvelteKit app that uses adapter-static, it assumes it's node/bun and runs it with that
• Right now, the deno adapter and anything else probably is broken in a similar way

[rubys]

I can use bun to build a nodejs output, and vice versa

OK. But can we flip this around? Perhaps for svelte we should treat the adapter as authoritative? If @sveltejs/adapter-node is in package.json, then use node for everything. Similarly for svelte-adapter-bun, and perhaps even svelte-adapter-deno.