Add a way to override url.origin when running nextjs app locally through a proxy like ngrok

[spennyp]

It is useful to run a frame server locally, and expose it via a proxy like ngrok to debug frames inside of Warpcast.

When running a nextjs app locally and using a proxy, url.origin will be localhost, which breaks the frame when used through the proxy. It would be ideal to have a way to override url.origin to use the proxy address.

frog/src/frog-base.tsx

Lines 268 to 270 in bd4c774

	const url = new URL(c.req.url)
	const assetsUrl = url.origin + parsePath(this.assetsPath)
	const baseUrl = url.origin + parsePath(this.basePath)

[ggomaeng]

You can pass origin to the frog options https://frog.fm/reference/frog#origin

[filipesoccol]

Using origin doesn't work for me behind a NGINX proxy. For some reason it turns back to "127.0.0.1" for images and redirection paths.

I've tested on the default node and bun templates. Both generate image files correctly on the domain, but the frog paths to images and routes are wrong. As I've reported here: https://discord.com/channels/1156791276818157609/1212219334370529370