feat(export): send reviewed line items to the ERP (contract v2)

[Fluory]

Ziel

Approved requests reach the ERP with their reviewed line items (description, quantity, unit, material, dimensions), not only the three header fields of contract v1. Today corrected line items are audited (#25, PR #42) but never exported.

Akzeptanzkriterien

• The ERP contract (contracts/erp-export.openapi.yaml) gains lineItems in a backwards-compatible way (new version or optional field – decision below) and the REST adapter + in-memory mock accept it.
• When a request with line items is approved, the export payload contains every line item with its reviewed value (latest correction of the current run, else the extraction).
• A line-item value that breaks an ERP limit blocks the approval with a readable message (same rule as exportLimitViolations for header fields) – never cut silently.
• The payload stays deterministic: a retry sends the same body under the same Idempotency-Key; exactly-once (idempotency key + unique export row + row lock) is unchanged.

Nicht Teil dieser Aufgabe

• Mapping to a real customer ERP (mock + contract only).
• Line-item editing beyond feat(review): line items and all formats in the review UI #25.

Betroffene Bereiche

• contracts/erp-export.openapi.yaml, src/features/export/{contract,payload,adapter}.ts, src/features/review (reviewed values per item)

Testplan

Kriterium	Prüfart
Contract + mock accept line items	contract/unit test
Payload carries reviewed line items	integration test (approve → export → mock record)
Limit violation blocks approval	integration test
Retry sends identical body	integration test (existing exactly-once suite extended)

Offene Entscheidungen

• Contract v2 (/v2/) or an optional lineItems field in v1? (API rule: breaking changes only with a new version.)
• ERP limits per line-item field (length, max. number of items).

Security/Privacy betroffen?

Public API contract change → human approval of the contract (SYSTEM.md §5). No new personal data beyond what is already exported.

Found during the overnight run (#2 morning report, review of PR #42).

[Fluory]

Claimed by @Fluory (Claude Code session) on branch claude/feat-erp-line-items-46. Orchestrator decision: optional lineItems field in contract v1 (additive, backwards compatible). Draft PR follows.

---

Generated by Claude Code