Add active-turn steering (#3394)

* feat(agents): add active-turn steering

Let users choose whether an immediate prompt interrupts or joins the active turn. The daemon owns exact-turn admission, provider delivery, safe fallback, and canonical timeline identity while queueing remains client-side.

* fix(agents): stabilize steering history and replay QA

* fix(agents): preserve steering timeline order

* fix(agents): reconcile resumed provider history

* fix(agents): serialize steering with cancellation

* test(agents): prove Claude multi-tool steering

* test(agents): force explicit history hydration

* fix(agents): flush output before steer admission

packages/app/e2e/browser/settings-toggle-tab-regression.spec.ts

@@ -12,7 +12,7 @@ async function pressSettingsToggleShortcut(page: import("@playwright/test").Page
 
 async function expectSendBehavior(
   page: import("@playwright/test").Page,
-  expected: "interrupt" | "queue",
+  expected: "interrupt" | "queue" | "steer",
 ) {
   await expect
     .poll(async () => {