fix(tui): move agent cycling to shift-tab (#37706)

Co-authored-by: Simon Klee <hello@simonklee.dk>

packages/tui/test/keybind.test.ts

@@ -0,0 +1,7 @@
+import { expect, test } from "bun:test"
+import { TuiKeybind } from "../src/config/keybind"
+
+test("binds agent cycling only to shift+tab by default", () => {
+  expect(TuiKeybind.Definitions.agent_cycle.default).toBe("shift+tab")
+  expect(TuiKeybind.Definitions.agent_cycle_reverse.default).toBe("none")
+})