Retrieve the full tracking timeline (status, carrier, ETA, event
history, and branding) by tracking number. The store is resolved from
the JWT, so there is no store segment in the path.

Canonical tracking_status values (exactly these):

• PRE_TRANSIT — label created, package not yet accepted by carrier
• TRANSIT — in transit
• DELIVERED — delivered
• RETURNED — returned to sender
• FAILURE — delivery failed, action required
• UNKNOWN — status not yet available

Out-for-delivery is not a distinct tracking_status — it is a
substatus of TRANSIT. When a package is out for delivery, read
tracking_status: "TRANSIT" with tracking_status_label: "Out for delivery" (tracking_status_substatus: "out_for_delivery").