Add integrated terminal + allow chat pane to anchor to the right side

[nvrcoder]

It would be a big usability boost if Dyad supported two things:

A built-in terminal pane – Most editors (Zed, Windsurf, Cursor) already support this, and it saves constant context-switching. Being able to run npm, git, supabase, or tests right inside Dyad would keep the workflow smooth.

Moveable panes – Specifically, the ability to move the AI agent pane so it can sit to the right of the preview (or wherever works best). Having flexible layout options makes it easier to fit different workflows and screen setups.