test(desktop): read only the open effort menu in effort-picker e2e (#8476)

## Summary
`menuValues()` in `claude-effort-picker.spec.ts` read every
`menuitemradio` on the page right after it opened a menu. Dropdown menus
stay mounted for their 100ms exit animation
(`POPOVER_RADIX_MOTION_CLASS`). That means the model menu, which
`pick()` had just closed, could still be in the DOM, and its rows ended
up in the effort list:

```
- Expected  - 0
+ Received  + 6
+   "Default model (Opus)", "Opus", "Claude Sonnet 5", "Haiku", "Claude Opus 4.8", "Custom model...",
    "Adapter default", "max",
```

The helper now waits for the trigger to report `aria-expanded="true"`,
then reads rows only from the menu named in its `aria-controls`. The fix
only touches the test; no product code changes.

### Related issue
The flake was introduced with the spec in #8059. In CI it failed
`Desktop Smoke E2E (2)` on #8473 (all three attempts,
[job](https://github.com/block/buzz/actions/runs/39336482034/job/118347673219))
and failed once before passing on retry on #8474.

### Testing
- **Forced repro.** I temporarily stretched the closed-menu exit
animation to 1500ms using `page.addStyleTag` (not committed):
  - Before: 5/5 failed with the same `toEqual` diff.
  - After: 5/5 passed.
- **Natural repeats.** I ran `--repeat-each` locally with 3–4 workers,
100 runs on each version:
  - Before: 3 failures from the menu-row leak.
  - After: 0.
- Both versions also had the same local-only startup timeouts (`waiting
for getByTestId('open-agents-view')`), which this change doesn't affect.
- **Full spec.** `pnpm exec playwright test --project=smoke
tests/e2e/claude-effort-picker.spec.ts`: 27 passed.
- `biome check` is clean.

Signed-off-by: Fizz <6be7be23ec5bba868f3e1db5ec86013d76bd1a293dce5b435a192158fec13641@buzz.block.builderlab.xyz>
Co-authored-by: Fizz <6be7be23ec5bba868f3e1db5ec86013d76bd1a293dce5b435a192158fec13641@buzz.block.builderlab.xyz>

desktop/tests/e2e/claude-effort-picker.spec.ts

@@ -137,7 +137,14 @@ async function payloadsFor(page: Page, command: string) {
 
 async function menuValues(page: Page, trigger: Locator) {
   await trigger.click();
-  const rows = await page.getByRole("menuitemradio").allTextContents();
+  await expect(trigger).toHaveAttribute("aria-expanded", "true");
+  // A menu that just closed stays mounted during its exit animation, so read
+  // only the menu this trigger controls.
+  const menu = page.locator(
+    `[id="${await trigger.getAttribute("aria-controls")}"]`,
+  );
+  await expect(menu).toBeVisible();
+  const rows = await menu.getByRole("menuitemradio").allTextContents();
   await page.keyboard.press("Escape");
   return rows;
 }