Browser: agent tabs join the panel I'm viewing, and the agent and I can share control

[praneeth-red]

Problem

1. When an agent opens a new browser tab, it pops up the floating mini player, even when I already have the browser panel open on another tab. I'd rather it appear as a tab in the panel I'm looking at.
2. Only one of us can control the browser at a time, so I have to take or release control before the agent can carry on.

Proposed solution

1. If the browser panel is open, add the agent's new tab there and switch to it, instead of floating it.
2. Let my clicks and typing work while the agent is using the tab, with the agent pausing while I'm typing.

Smallest useful scope

Point 1 alone.