Builds the Apollo link context so requests include the user's Bearer token.
Used internally by useAuthQuery / useAuthMutation; you typically don't call this directly.
Parameters
Optionaltoken: string|null
The JWT access token. If null/undefined, returns undefined (no auth header).
Builds the Apollo link context so requests include the user's Bearer token. Used internally by
useAuthQuery/useAuthMutation; you typically don't call this directly.