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-trajectory/tests/views.spec.tsx

@@ -109,6 +109,7 @@ function mount(slots: SlotsService, nodes: ConversationSnapshot['nodes'] = NODES
   const sessionSnapshot = createSnapshotStore({
     running: false, removed: false, promptError: null, nodes,
     partial: null, runningCalls: [] as ConversationSnapshot['runningCalls'],
+    todos: [] as ConversationSnapshot['todos'],
   })
   const useSession = bindSnapshotSelector(sessionSnapshot) as unknown as UseSession<ConversationSnapshot>
   const chat = createChatStore().create()