feat: add plan4.md

Author: alexhancock

ui/desktop/plan4.md

@@ -0,0 +1,4 @@
+* we are improving the compaction and summarization ux in this app
+* review the diff to date by running: git diff main
+* i want to make an improvements now
+* right now if I try to compact a conversation twice, it errors the second time because the rust server handling the compaction requests doesn't recognize the compactionMarkers. summarizationRequested messages used to be inserted, so this needs to be normalized across both rust and ts to the new name: compactionMarker