[Mobile] Add Browser Preview for remote web development via T3 Connect

[NANAMINER]

Problem

One of the most useful features in T3 Code Desktop for me is Browser Preview.

When I'm working on a web app or a browser game, the workflow is very convenient:

1. The agent starts the dev server.
2. I open Browser Preview.
3. I immediately inspect the result without leaving T3 Code.
4. I continue giving feedback to the agent.

However, when I connect to the same environment from the T3 Code mobile app, Browser Preview is not available.

This makes the remote/mobile workflow much less useful. I can control the agent, inspect the conversation, files, terminal, etc., but I cannot conveniently open the web app the agent is actually working on.

Proposed behavior

Add Browser Preview to the mobile app on both Android and iOS.

Ideally, when a dev server is running on the host machine, T3 Code Mobile should be able to expose/open it through the existing T3 Connect connection.

For example:

• Agent starts Vite on localhost:5173
• Desktop T3 Code can open it in Browser Preview
• Mobile T3 Code connected to the same environment should also offer Preview
• Tapping it opens the running app directly inside T3 Code Mobile

The user should not have to manually configure a separate tunnel or expose every dev-server port to the internet.

Useful UX

At minimum:

• Detect available dev-server / preview ports
• Show a Preview/Browser button in the mobile thread
• Open the preview inside the mobile app
• Allow refresh / back / forward
• Allow opening the same URL in the system browser

It would also be useful to have:

• viewport/device controls
• reload when the app rebuilds
• the same preview URL preserved while switching between the thread and preview

Why this matters

T3 Code Mobile is especially useful when I want to keep development running on my computer while controlling it from my phone.

For web development, seeing the actual result is a fundamental part of that workflow.

Right now I can tell the agent to change the UI from my phone, but then I cannot conveniently look at what it changed without setting up another way to reach the dev server.

Browser Preview on mobile would make T3 Connect feel much closer to actually using T3 Code remotely rather than only remotely controlling the chat.

Related

This is different from #3609, which is about Android/iOS emulator preview inside the desktop app.

Also related to the broader goal of improving feature parity between desktop and mobile, including Discussion #14038 (Edit from here / checkpoint revert on mobile).

[PixPMusic]

Most of this seems to be implemented now through #15328. On mobile, once an agent opens a browser tab, the preview appears and I can use it.

The remaining gap seems to be opening it myself: a Browser entry in the thread’s three-dot overflow menu, plus the ability to open new tabs and navigate to a URL without starting an agent turn.