When models arrive late the first available model is selected as the default in Agents Window

[DonJayamanne]

As reported by Harald

• The BYOK models arrived early
• I.e. there was just one model in the model picker
• Other models (including Auto) arrived 12s later
• Hence the BYOK was setup as the selected item
• What made this worse is, the existing code then seems to mark this as a user selection and treas this as the default for all new Agent Window sessions

https://vscodeteam.slack.com/archives/C0AKR94N3CK/p1784227881592419