fix(gui): the collapsed plan hint accounts for parallel active items

Lifting the single-in_progress cap makes a list shape reachable that the
web surfaces never received. Two sites derived their one-line summary with
todos.find(t => t.status === 'in_progress') — the collapsed TodoPanel header
and the todo_write row — which was total under the old cap and silently
dropped every active item but the first once several could match: a plan
with three running tasks collapsed to the name of one. The expanded list
was always correct, so neither PR's tests covered it.

Both sites now take planSummary in contract/todo-plan-model.ts, the
domain-shared face both the skeleton and toolviews domains may import; the
duplicated derivation was why one find could be fixed while the other
stayed wrong. The hint names the first active item and suffixes +<n> for
the rest, so the collapsed line reports how many tasks are running.

The web fixture's todo sample now runs two items in_progress, so the
assembled web transcript replays a parallel plan: the row reads
'1/4 已完成 · 实现 fixture 样本 +1' over the built bundles.

packages/client/connection/tests/fixture.spec.ts

@@ -84,6 +84,10 @@ describe('createFixtureApi', () => {
     const times = events.slice(todoAt - 1, todoAt + 2).map(e => e.time)
     expect(times[0]).toBeLessThanOrEqual(times[1] ?? 0)
     expect(times[1]).toBeLessThanOrEqual(times[2] ?? 0)
+    // The sample is a parallel plan: the tool permits several in_progress, so
+    // the surfaces fed from here are exercised against more than one active item.
+    const snapshot = events[todoAt] as { data: { todos: { status: string }[] } }
+    expect(snapshot.data.todos.filter(t => t.status === 'in_progress')).toHaveLength(2)
   })
 
   it('create adds a session and pushes host/session-added to open host streams', async () => {