ENH-008 — Replace `orderedBy` Free-Text with Structured User Reference 🟠

[hajk1]

FreightOrder.orderedBy is a free-text String with only a @NotBlank constraint. Any arbitrary
value is accepted ("me", "ops-team", ""), there is no referential integrity, and orders
cannot be queried by a specific operator. This issue replaces the string field with an Operator
entity that represents an internal system user.

New entity: Operator

• id — BIGINT PK
• username — VARCHAR(50), UNIQUE, NOT NULL
• fullName — VARCHAR(100)
• email — VARCHAR(150), UNIQUE, NOT NULL
• active — BOOLEAN, DEFAULT TRUE
• createdAt / updatedAt — timestamps (via BaseEntity)

New endpoints:

• POST /api/v1/operators — create an operator
• GET /api/v1/operators — list all operators
• GET /api/v1/operators/{id} — get a single operator

Changes to FreightOrder:

• Remove String orderedBy
• Add @ManyToOne(fetch = LAZY) Operator operator (FK operator_id)
• CreateFreightOrderRequest: replace orderedBy: String with operatorId: Long
• FreightOrderResponse: expose operatorId and operatorUsername

Migration:

• Flyway V2__add_operators.sql — creates the operators table and adds the operator_id column
  to freight_orders
• If seed data contains existing orderedBy strings, the migration should insert corresponding
  Operator rows and back-fill the FK

Hints:

• This is a breaking API change — orderedBy is removed entirely, not deprecated alongside
  operatorId
• Operator will be the natural entity to link to an auth identity if authentication is introduced
  later; keep the model clean for that

Acceptance criteria:

• Operator entity, repository, service, and controller created
• POST, GET (list), GET (by id) endpoints working under /api/v1/operators
• FreightOrder.orderedBy (String) removed; operator (@ManyToOne) added
• CreateFreightOrderRequest uses operatorId: Long
• FreightOrderResponse exposes operatorId and operatorUsername
• V2__add_operators.sql Flyway migration present
• FreightOrderControllerTest and FreightOrderServiceTest updated to use operatorId
• Existing seed data migrated in the SQL file if applicable
• Code is formatted

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