[FEATURE]: Display the exact url opencode is failing to connect to

[gregid]

Feature hasn't been suggested before.

• [x] I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Existing error when opencode can't connect to the model is:

Error: Unable to connect. Is the computer able to access the url?

I propose more meaningful message that would quickly allow to check the url:

Error: Unable to connect. Is the computer able to access the following url: http://example.org ?