Mode changes does not work with ACP

### Describe the bug

I have found two bugs related to modes in ACP:

* The agent cannot leave plan mode. Once we start plan mode and then plan is done, it should [propose to execute the plan and swap modes](https://agentclientprotocol.com/protocol/session-modes#exiting-plan-modes)

* Autopilot mode has no effect. I am unsure if this is related to the separation between autopilot vs /allow-all, but it still always asks for permission. We may need autopilot to automatically enable /allow-all for ACP

### Affected version

1.0.35

### Steps to reproduce the behavior

I was able to reproduce those bugs both in Zed and Tidewave.

1. Enter plan mode, ask it to plan and execute the plan. You see no tool request arrives.
2. Simply choose autopilot and ask it to make changes and run commands. You see it will request tool permissions.

Glad to provide any more info. :)

### Expected behavior

_No response_

### Additional context

_No response_