Better Remote Connections for Desktop

**What problem would this solve?**
* The remote backend feature of the desktop app has several issues
* It does not follow redirects
* It cannot supply a client cert for hosts that require mTLS
* It does not have a way for the user to test the connection before enabling it
* It requires a new window, but when the connection doesn't work for any reason the window just never opens, it times out and you get a system dialog saying to disable it and re-open. There is no way to figure out what the error with the connection is

**What would a good outcome look like?**
* A version that connects in the same window
* A "test connection" button that shows what's working and any errors encountered

**Possible approaches**
* Route the ACP connection through the `main.ts` node process side for more control over the connection (certs, redirect following, etc) and relay that info to the renderer side

**Additional context**
N/A

- [x] I have verified this does not duplicate an existing feature request

Do not begin implementation until the issue reaches **Ready** on the [Goose Issues board](https://github.com/orgs/aaif-goose/projects/1).

The issue mentions routing the ACP connection through the main.ts node process. Start by examining the desktop app's remote backend code, likely in the main.ts file and related IPC (inter-process communication) modules. Look for existing connection handling and error reporting. A 'test connection' button would need UI changes in the renderer and new IPC messages to the main process. 'Done' means the connection can follow redirects, support mTLS client certs, and show diagnostic errors in the same window.

索引モデルが issue の本文から書いたものです。