Refactor useOnClerkEvent hook for better stability and API safety

[coderabbitai]

Description

The useOnClerkEvent hook in src/lib/useOnClerkEvent.ts could be improved to:

1. Stabilize callback - Prevent resubscription on every render by using a ref to store the latest callback
2. Guard for API presence - Check that clerk.addListener exists before attempting to use it
3. Pass through original event - Forward the complete event object instead of reconstructing {user, session, client}

Current Issues

• Hook resubscribes on every render when callback identity changes
• Assumes clerk.addListener exists without checking
• Strips event metadata by reconstructing the event object

Proposed Changes

• Use useRef to stabilize the callback reference
• Add type guards for clerk and clerk.addListener
• Pass the original event object directly to the user callback

Context

This issue was identified during code review of PR #184.

References:

• PR: invalidate query cache on auth change #184
• Comment: invalidate query cache on auth change #184 (comment)