[Analytics] Account Details Menu Opened event never fires

## Description
The event `Account Details Menu Opened` is defined as a constant in `MetaMetrics.events.ts` but is never imported or called in `AccountsMenu.tsx`. The component has `useAnalytics()` already wired up and fires other analytics events correctly (buy, notifications, settings, lock, QR scanner) — the screen-open event is simply missing.

**File:** `app/components/Views/AccountsMenu/AccountsMenu.tsx`
**Owner:** `@MetaMask/mobile-core-ux`

## Steps to Reproduce
1. Open the Accounts Menu in MetaMask Mobile.
2. Check Mixpanel for an `Account Details Menu Opened` event.

## Expected Result
An `Account Details Menu Opened` event fires in Mixpanel each time the AccountsMenu mounts/gains focus.

## Actual Result
Zero events recorded. Confirmed via Mixpanel QA project (project `3354001`, report `Mobile Core UX` #91404720) — the event has 0 count across all time.

## Fix
Add a `useEffect` (or `useFocusEffect`) at the top of `AccountsMenu.tsx`:
```ts
trackEvent(
createEventBuilder(MetaMetricsEvents.ACCOUNT_DETAILS_MENU_OPENED).build()
);
```

## Severity
Medium

---
*Filed via Claude bug reporter*

Start in app/components/Views/AccountsMenu/AccountsMenu.tsx and inspect the existing useAnalytics setup and nearby event calls. Check MetaMetrics.events.ts for the Account Details Menu Opened constant, then verify that opening or focusing AccountsMenu produces the event and that existing analytics behavior remains unchanged.

Written by the indexing model from the issue text.