[ZEPPELIN-6384] Fix dropdown menu item links not clickable in full area

[tbonelee]

What is this PR for?

Summary

• Fixed dropdown menu items in header where only text was clickable instead of the full item area
• Changed routerLinkActive to nzMatchRouter for proper NG-ZORRO integration
• Added CSS pseudo-element to expand clickable area of anchor tags

Cause

• Likely due to NG-ZORRO dropdown menu item anchor tag style changes that reduced the clickable area to just the text content.

Changes

• Updated header.component.html: Replace routerLinkActive with nzMatchRouter directive
• Updated global.less: Add ::before pseudo-element to .ant-dropdown-menu-item > a to expand clickable area using absolute positioning

What type of PR is it?

Bug Fix

What is the Jira issue?

https://issues.apache.org/jira/browse/ZEPPELIN-6384

Questions:

• Does the license files need to update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No