skill: add sqlAnalystSkill

## Area

`skills` package

## Why

Natural language → SQL with safety rails + dialect awareness.

## Notes

Pairs with sqliteQueryTool + postgresTool.

## Checklist

- [ ] Implementation
- [ ] Tests (unit + contract where applicable)
- [ ] Docs page under `/docs/reference` + deep-dive under the relevant tab
- [ ] Changeset (patch or minor)
- [ ] Example recipe cross-linked