Add a `?status=` filter to `GET /api/v1/settlements`, wired through `settlementService.list`

[Jagadeeshftw]

📌 Description

Settlement.status ("pending" | "executed" | "cancelled") is central to the settlement lifecycle, but SettlementService.list only accepts anchor/asset filters — there's no way to ask GET /api/v1/settlements for, say, only pending settlements, even though routes/metrics.ts already computes pendingSettlements internally via the same kind of filter.

🧩 Requirements and context

• Extend SettlementService.list's filters parameter to accept an optional status, validated against the SettlementStatus union (reject anything else with 400).
• Wire ?status= through routes/settlements.ts's GET / handler.
• Combine correctly with existing ?anchor=/?asset= filters, sorting, and pagination.

🛠️ Suggested execution

• Modify src/services/settlementService.ts's list to accept and validate status.
• Modify src/routes/settlements.ts's GET / handler to parse req.query.status.
• Update src/openapi.ts's /api/v1/settlements GET parameters.
• Add tests in src/services/settlementService.test.ts and src/routes/settlements.test.ts covering each status value and an invalid value.

✅ Acceptance criteria

• GET /api/v1/settlements?status=pending returns only pending settlements.
• An invalid ?status= value (not one of the three valid statuses) returns 400.
• Combines correctly with existing filters, sort, and pagination.

🔒 Security notes

N/A — read-path filter over already-exposed settlement lifecycle data.

📋 Guidelines

• Minimum 95% test coverage
• Clear documentation
• Timeframe: 96 hours