[Feature]: Surface the device toolbar as a preview toolbar button

[glauber-sampaio]

Before submitting

• I searched existing issues and did not find a duplicate.
• I am describing a concrete problem or use case, not just a vague idea.

Area

apps/web

Problem or use case

The device toolbar is only reachable through the three-dot menu in the preview chrome row. It is the fastest way to check a layout at a phone or tablet size, but it sits two clicks deep behind a menu you have to already know to open.

Everything else on that row that changes what the preview shows is a visible icon — annotate, screenshot, floating preview:

I used T3 Code for a while before finding out the device toolbar existed.

Proposed solution

Promote it to an icon button in the chrome row, next to the annotation button, with a pressed state while a fixed viewport is active. Moving it rather than duplicating it keeps the menu for actions that have no icon.

A preview.deviceToolbar command would also make it bindable. mod+shift+d is free outside the terminal, which uses that chord for terminal.splitVertical; Chrome's mod+shift+m is already the model picker here.

Why this matters

Responsive checking is a normal part of working on a page in the preview, and it is currently the only such action hidden in a menu.

Smallest useful scope

The toolbar button alone. The keybinding is separable and could follow #4641.