Username mentions fail in GLQL embedded views when username starts with a number

Problem

When displaying GLQL query results in embedded views, username references fail with an "Invalid reference" error if the username begins with a number, despite such usernames being valid in GitLab.

Current Behavior

• In embedded GLQL views, usernames starting with numbers throw "Invalid reference" errors
• Changing the username from @16c73 to "16c73" (without @) works correctly
• Usernames starting with letters work fine with @ syntax in embedded views
• The username @16c73 is valid elsewhere in GitLab

Expected Behavior

The GLQL embedded view renderer should handle username references consistently, supporting @ mentions for all valid usernames including those starting with numbers.

Root Cause Analysis

This is an oversight in the username token checker. Usernames cannot start with a special character, but the username token checker also doesn't allow mentioning a username that starts with a number, creating an unintended restriction.

Proposed Solution

Remove the restriction in the username token checker to allow username references that begin with a number.