docs(skill): sandbox datasets, long flags, and WORKFLOWS

- SKILL: document sandbox run vs active sandbox, datasets schema
  (datasets.<sandbox_id> vs main), full_name/FULL NAME, list scope,
  sandbox context for queries, PostgreSQL quoted identifiers
- SKILL: use long CLI flags (--workspace-id, --output, --connection-id)
- WORKFLOWS: new Sandboxes and datasets section; align Chain, Model
  refresh, History, Indexes examples; cross-cutting pointers

Author: eddietejeda