better plan widget feedback providing UX

[justschen]

overview:

• the way to provide feedback to the plan currently opens the editor to the side (and in the agents window, opens up the editor modal)
• there should be a better way of providing feedback to individual lines + overall feedback for the plan

solution:

• edit in line IN the widget
• add a setting that lets you edit in the editor if you really want to

verification steps

• make sure to test the following: copilot cli + agents window, copilot cli + panel chat, claude agent + agents window, claudeagent + panel chat
• make sure that the chat.planReview.inlineEditor.enabled is enabled (true)
• ask for plan creation in cli (or in cluade, switch the permissions picker to plan mode)
• once a plan is created, click on edit or provide feedback. it should open the editor inline.
• try edting the plan and submitting. or adding comments. or adding an overall feedback piece
• make sure that the plan.md file reflects these changes once you submit your feedback or edit!

[justschen]

fixed by #314332 and #315579