[Bug]: Sidebar V2 (desktop): selecting a remote (Tailscale) project in the new-thread picker opens an existing thread — no way to start a new thread on a remote environment

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/desktop

Steps to reproduce

1. Desktop app with Sidebar V2 enabled, plus a remote backend (Linux box, reached via Tailscale) that already has several projects and threads.
2. Open the new-thread project picker. Projects from both environments are listed (mixed together, with no environment indicator — you can only tell them apart by the /Users/... vs /home/... paths).
3. Select a project that lives on the remote environment.

Expected behavior

A new thread draft opens on that remote project, same as when selecting a local project.

Actual behavior

The app navigates to an existing thread of that remote project instead. There is no path from the Sidebar V2 UI to create a new thread on a remote project — new threads can only be started on local projects.

Additional context

Possibly related to #5289 (non-primary T3 Connect/SSH/Tailscale environments missing provider icons in Sidebar V2) — remote environments generally seem second-class in the V2 sidebar. The lack of any environment label in the picker (step 2) may be worth its own issue; happy to file separately if useful.

Start in apps/desktop by tracing the Sidebar V2 new-thread project picker and how it handles projects from remote environments. Reproduce with a remote project that already has threads; done means selecting it opens a new thread draft rather than navigating to an existing thread.