Improved ES|QL Generation

Get a valid ES|QL query on the first attempt more often. Better schema grounding, expanded eval coverage for complex patterns like LOOKUP JOIN and multi-index queries, and targeted tooling fixes cut the first-pass failure rate that adds latency and erodes trust.

**What the feature is**
Quality improvements to generate_esql, including stronger schema grounding and expanded eval coverage for complex patterns like LOOKUP JOIN and multi-index queries.

**Why it matters**
The agent returns a valid query on the first attempt more often. That removes the latency and eroded trust that come from retries, and stops bad queries from slipping through silently in automated workflows.

**Use cases**
Automated query workflows, analytics agents, anything that generates ES|QL.