Add withAuth Helper Function

[nicknisi]

Add new withAuth function for simplified auth data access

Purpose

This PR adds a new withAuth function that provides a simpler way to access authentication data in child routes without wrapping loaders. It complements the existing authkitLoader pattern rather than replacing it.

Implementation

• Added withAuth function that accepts LoaderFunctionArgs and returns auth data
• Function reads from the session cookie without handling refresh operations
• Added developer warning when no session cookie is found
• Added token expiration warning to help detect potential timing issues
• Maintained the same auth data structure returned by authkitLoader

Benefits

• Reduces boilerplate in child routes that only need to read auth data
• Simplifies access to user info, permissions, roles and tokens
• Improves code readability by separating auth data access from loader logic
• Works alongside existing patterns without breaking changes

Usage Example

export async function loader({ request }: LoaderFunctionArgs) {
  const { user, permissions } = await withAuth({ request });
  
  // Use auth data without wrapping the entire loader
  const data = await fetchSomeData();
  
  return json({ data });
}

Design Considerations

The withAuth function assumes that authkitLoader is used in a parent/root route to handle session refresh. It focuses on reading auth data rather than maintaining the authentication lifecycle.

Fixes #19