Validate geographic data contributions against the CSC database schema. Use this skill whenever you encounter a PR that adds, modifies, or deletes data in the contributions/ directory. Trigger on: validate, check, review, verify, audit, inspect, or assess any data contribution, PR review requests, schema compliance checks, field validation, or when someone says "is this correct", "check my data", "validate this", or "review my PR". Also use when asked about required fields, allowed values, or data format rules. Read schema-rules.md in this directory for the complete field specification.