Agent Skills: ring:migrating-to-lib-observability

Migrating a Lerian Go app off lib-commons observability imports (deprecated shims or removed APIs) to lib-observability via a fixed mapping table, then bumps go.mod and validates the build; ring:backend-go applies the edits. Covers log/zap/runtime/assert, opentelemetry/tracing, HTTP middleware, context helpers, and direct systemplane import moves. Use when lib-commons observability imports remain or the build breaks on removed APIs.