Add Save-as-plan action on assistant messages that writes a markdown plan
into the project plans directory and suggests a title from the text. Plan
view opens a specific saved plan via targetPath, supports inline edits, and
can kick off improve or implement flows in a new or worktree session.
Ship the matching hidden magic prompts (plan.todo/improve/implement) so the
instructions applied by these flows are visible and editable in the Magic
Prompts page.
Remove the plan editor font override, CodeMirror now uses the app font stack.