feat(plan): iterative planning & plan review

[KibbeWater]

What does this PR do?

This PR adds two new features:

• Iterative Planning, something which for example Claude Code and I believe Cursor as well which will keep iterating on one and the same plan document instead of writing it to the conversation history, losing context between iteration, etc...

• Plan Review / Summary, after iterating on the plan, it will request to exit planning mode. When it does this it'll let you approve/reject the plan, give an optional reason, or dismiss it entirely and interrupt the flow. Gives you an easy way of looking through the entire plan before executing on it.

How did you verify your code works?

Basic tests in plan mode via TUI and Web interface by planning new features, smaller changes and more in real projects