[GFI] Custom Tracking Numbers

**Description:**
Allow users to define and assign custom tracking numbers for orders and other entities.

**Tasks:**
- Ensure support for manual or auto-generated tracking numbers.
- Ensure uniqueness within the company scope.
- Display custom tracking numbers in order and entity listings.

**Acceptance Criteria:**
- Users can set or override tracking numbers.
- Tracking numbers are unique and searchable.
- Tracking numbers show in detail and label views.

**References:**
- Related models: `Order`, `Entity`.
- See `HasTrackingNumber` trait