New thread should skip the project picker when "No project" is the only other choice

[OlegBezr]

Problem

I have one project. Every time I click New thread (or press the new-thread shortcut), T3 Code opens the "New thread in" picker and asks me to choose between my project and No project. With one real project, I always pick the same row, so the picker is an extra step every time.

The app already skips the picker when only one project is open. But after you start one "No project" thread, T3 Code keeps a hidden scratch project for it. That scratch project counts as a second open project, so the skip never happens again.

Proposal

When T3 Code decides whether to show the picker, ignore the scratch project behind "No project":

• One real project open: start the new thread in that project directly, like it does today when no scratch project exists.
• "No project" stays one keystroke away: ⌥⌘N (chat.newWithoutProject) and the picker row still work.
• Two or more real projects: no change, the picker opens.

From a "No project" thread, a new thread stays in "No project", the same as Shift+click does today.

I opened a small PR with this change: #29798. It is a few lines in the sidebar and shortcut decision, plus a test row.

Question: fix or setting?

Would you prefer a boolean setting instead of the fixed rule? For example, "Include No project when choosing where a new thread starts" in Settings, off by default:

• Off (default): the behavior in the PR. With one real project, New thread starts there directly.
• On: the current behavior. The picker opens every time "No project" exists.

I did the fixed rule first because it keeps the one-project skip working as designed, with no new option. If you prefer the setting, I will update the PR and add Settings screenshots.