feat(gui): todo display — TodoPanel plan strip + todo_write toolview row

TodoPanel pins above the composer (776px card axis), hidden while empty,
collapsible with the active item as the collapsed hint; status glyphs
mirror the TUI plan panel. todo_write rows render a plan-flavored summary
(counts + active item) via the toolview registry, generic fallback on
malformed args. Existing fake snapshots gain the required todos field.

packages/client/ui-conversation/tests/chat-stats-bash-sample.spec.tsx

@@ -28,7 +28,7 @@ function snapshotBase(): ConversationSnapshot {
   return {
     sessionId: SID, nodes: [], foldDegraded: false, partial: null, runningCalls: [],
     pending: [], running: false, removed: false, openState: 'open', openError: null,
-    hasMore: false, loadingOlder: false, promptError: null, lastAgentError: null,
+    hasMore: false, loadingOlder: false, promptError: null, lastAgentError: null, todos: [],
   }
 }