agent ui: add a clickable new-session menu entry

Same gap #4611 fixed for logout: the Preact rewrite's StatusChips menu
never picked up new-session as a click path, only /new-session typed
twice into the terminal. postNewSession already existed in
termActions.ts. Wire it into the status menu with the same arm-then-
confirm click pattern logout/cancel-turn already use.

Closes #4612

frontend/packages/agent/src/Root.tsx

@@ -27,7 +27,11 @@ import { fmtAge, fmtTokens } from "./lib/format.js";
 import { resolveDashboardBase } from "./lib/dashboardBase.js";
 import { submitPauseResume } from "./lib/pauseAction.js";
 import { postModel, postEffort } from "./lib/modelEffort.js";
-import { postCancelTurn, postLogout } from "./lib/termActions.js";
+import {
+  postCancelTurn,
+  postLogout,
+  postNewSession,
+} from "./lib/termActions.js";
 import type { TokenUsage } from "./types.js";
 
 type OpenPanel = "inbox" | "todos" | null;
@@ -225,6 +229,7 @@ export function Root() {
               onTogglePause={() => {}}
               thinking={false}
               onCancelTurn={() => Promise.resolve()}
+              onNewSession={() => Promise.resolve()}
               onLogout={() => Promise.resolve()}
             />
           </Header>
@@ -332,6 +337,15 @@ export function Root() {
                 refresh();
               })
             }
+            onNewSession={() =>
+              postNewSession().then((r) => {
+                if (!r.ok)
+                  liveStreamRef.current?.pushNote(
+                    `✗ /new-session failed${r.detail ? ": " + r.detail : ""}`,
+                  );
+                refresh();
+              })
+            }
             onLogout={() =>
               postLogout().then((r) => {
                 if (!r.ok)