adapt todo display to the slash/input/session architecture

- TodoPanel mounts through a 'conversation.input.dock' list entry
  (todoDockEntry, QueueDock posture, order -1 above the queue rows) instead
  of a ConversationRoot hardcode; the inner component is unchanged and takes
  useSession from the dock entry's standard kit.
- The verify-todo-display.mjs chromium probe is replaced by an assembled
  keyless snapshot (apps/web/tests/todo-display.snapshot.ts, the
  code-mode-fixture idiom) pinning the TodoRow summary/state, the dock
  panel content, and the collapse round-trip over built bundles.
- Fake snapshots across specs gain the todos field; bilingual note/READMEs
  updated for the dock mount and the snapshot.

packages/client/ui-conversation/tests/input-scenarios.spec.tsx

@@ -111,7 +111,7 @@ async function scopedBench(register?: (slash: SlashService) => void) {
   const wiring = shell
   const sessionStore = createSnapshotStore<ConversationSnapshot>({
     sessionId, nodes: [], foldDegraded: false, partial: null, runningCalls: [], codeDispatches: new Map(),
-    pending: [], queue: [], running: false, composerPhase: 'active', removed: false,
+    pending: [], queue: [], todos: [], running: false, composerPhase: 'active', removed: false,
     openState: 'open', openError: null, hasMore: false, loadingOlder: false,
     promptError: null, blank: false, lastAgentError: null,
   })