Closes #161

Description

This PR resolves the issue where LiquidityRepository exposed byAsset(asset) but had no symmetric byAnchor(anchor) to list every asset balance held by a single anchor, making it difficult for the routing layer to efficiently query an anchor's total balances.

Changes

• LiquidityRepository: Added byAnchor(anchor: string): LiquidityEntry[] which mirrors the byAsset method.
• LiquidityService: Added listByAnchor(anchor) method to fetch all balances for an anchor.
• Routes: Added the GET /api/v1/liquidity/anchors/:anchor route to expose the functionality, carefully ordered to avoid shadowing the existing /:asset endpoint.
• OpenAPI: Updated the OpenAPI specs in src/openapi.ts to document the new GET /api/v1/liquidity/anchors/{anchor} endpoint.
• Tests: Added extensive test coverage in src/repositories/liquidityRepository.test.ts, src/services/liquidityService.test.ts, and src/routes/liquidity.test.ts.

Testing

• Tests added verify byAnchor works correctly and returns the appropriate entries.
• Verification ensures GET /api/v1/liquidity/anchors/:anchor does not conflict with GET /api/v1/liquidity/:asset.
• Test suite (328 tests) passed successfully.

Security notes

No new write access added; this relies on an existing read-only filter pattern that exposes data already accessible (less efficiently) via the unfiltered endpoint.