Mobile: run project actions and open the in-app browser without an agent

[jsrodrigo]

On mobile, project actions and the in-app browser are only reachable through an agent.

What I see (iOS app, server 0.1.1-nightly.20261017.3238): the thread header shows terminal, files and git. There is no actions (scripts) menu and no globe / browser toggle. A browser tab only appears, as the "N tab open" pill above the composer, when an agent opens one with preview_open.

Why it matters: with a project action like python3 -m http.server 4180 plus previewUrl: http://localhost:4180/research/index.html, T3 becomes a great way to browse personal HTML notes and docs on the phone. Links work in the collaborative preview. Today, starting the server from the mobile terminal is easy, but there's no way to open the preview without asking an agent.

Ask:

1. An actions menu on mobile to run project scripts.
2. A way to open the in-app browser on mobile (address bar, or the "Local servers" list that desktop shows in the empty state, including configured previewUrls).

Related: #20887 (relative links in file-tree HTML), #5221 (autoOpenPreview has no effect).