XY-790: [ELF hardening 2/4] Add utoipa and Scalar API contract surface

[yvette-carlisle]

Summary

• generate the ELF API OpenAPI contract with utoipa and serve it from /openapi.json
• serve Scalar API documentation from /docs using the generated contract
• document the local contract routes and add route-level tests for critical OpenAPI paths, including default ingestion-profile GET/PUT
• update the cargo-make vstyle wrapper to pass the required language argument used by the repo gate

Verification

• cargo make fmt
• cargo make lint-fix
• cargo make checks