style: add hover effects to account menu button in multichain account cell (#37576)

## Description

Fixes the kebab button hover highlighting issue where the button would
become highlighted when hovering anywhere on the account cell.

## **Changelog**

- Removed kebab button styling from account cell hover state
- Added direct hover state to kebab button component
- Kebab button now only highlights when directly hovered

CHANGELOG entry: null

## **Related issues**

Fixes: #35985

## **Manual testing steps**

1. Open the account list
2. Hover an account row -> the kebab menu keeps its default style
3. Hover the kebab menu -> it gets highlighted

## **Screenshots/Recordings**

<!-- If applicable, add screenshots and/or recordings to visualize the
before and after of your change. -->

### **Before**

<img width="394" height="117" alt="image"
src="https://github.com/user-attachments/assets/1c2450fe-0fd1-4abc-b28a-c069dcf32f7e"
/>


### **After**


https://github.com/user-attachments/assets/34e6dc54-32c7-44ee-87e1-685589e053e4


## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask
Extension Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I’ve included tests if applicable
- [x] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Shift kebab/menu button highlight from cell hover to direct button
hover, keeping only name color change on cell hover.
> 
> - **UI (SCSS)**
> -
`ui/components/multichain-accounts/multichain-account-cell/index.scss`
> - Remove hover styling targeting
`multichain-account-cell-popover-menu-button` and its icon from the cell
hover state; retain account name color change on cell hover.
> -
`ui/components/multichain-accounts/multichain-account-menu/index.scss`
> - Add direct `:hover` styles to
`multichain-account-cell-popover-menu-button` and its icon to control
highlight behavior.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
3202e6a. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: Fabio Bozzo

ui/components/multichain-accounts/multichain-account-cell/index.scss

@@ -23,13 +23,5 @@
     .multichain-account-cell__account-name {
       color: var(--color-primary-default);
     }
-
-    .multichain-account-cell__end_accessory .multichain-account-cell-popover-menu-button {
-      background: var(--color-primary-muted);
-    }
-
-    .multichain-account-cell__end_accessory .multichain-account-cell-popover-menu-button-icon {
-      background-color: var(--color-primary-default);
-    }
   }
 }

ui/components/multichain-accounts/multichain-account-menu/index.scss

@@ -2,6 +2,14 @@
   cursor: pointer;
   width: 28px;
   height: 28px;
+
+  &:hover {
+    background: var(--color-primary-muted);
+
+    .multichain-account-cell-popover-menu-button-icon {
+      background-color: var(--color-primary-default);
+    }
+  }
 }
 
 .multichain-account-cell-popover-menu {