Add settlement volume totals (sum of `amount`/`fee`) to the `routes/metrics.ts` snapshot, not just counts

[Jagadeeshftw]

📌 Description

routes/metrics.ts's snapshot() reports settlements/pendingSettlements as counts and totalLiquidity as a pool-wide sum, but never sums settlement amount/fee — an operator can't currently see total value settled or total protocol fees collected without fetching every settlement and summing client-side.

🧩 Requirements and context

• Add totalSettledAmount and totalFeesCollected (or similarly named) fields to MetricsSnapshot, computed from executed settlements only (fees/amounts of pending/cancelled settlements shouldn't count toward "collected").
• Keep existing fields (anchors, activeAnchors, pools, totalLiquidity, settlements, pendingSettlements) unchanged.

🛠️ Suggested execution

• Modify src/routes/metrics.ts's MetricsSnapshot interface and snapshot() function to compute the new sums from deps.settlements.list() filtered to status === "executed".
• Update src/openapi.ts's /api/v1/metrics entry to document the new fields.
• Add tests in src/routes/metrics.test.ts covering a mix of pending/executed/cancelled settlements to verify only executed ones contribute to the new totals.

✅ Acceptance criteria

• GET /api/v1/metrics includes correct totalSettledAmount/totalFeesCollected computed only from executed settlements.
• Existing fields and GET /api/v1/metrics/history snapshot shape remain backward compatible (new fields simply added).

🔒 Security notes

N/A — read-only aggregate metric over already-exposed settlement data.

📋 Guidelines

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