Add schema contract tests

## Problem
Schema drift between the two Skills and the spec would break consumers silently.

## Goal
Tests that validate both Skills' structured output against the versioned schema.

## Scope
- Validate sample outputs from both Skills against the schema.
- Assert shared fields carry identical meaning.
- Fail on unversioned or schema-invalid output.

## Non-goals
- Consumer-side integration tests.

## Acceptance criteria
- Both Skills' outputs validated in tests.
- Cross-Skill field parity asserted.
- Unversioned or invalid output fails the suite.

## Dependencies
Depends on #69, #70 (both open). Parent: #44.

## Validation
- Test run included in standard validation.

No file paths are named. Start by reading the versioned schema and the work in #69 and #70, then locate the standard validation entry point. The work is done when both Skills' sample outputs are schema-validated, shared fields have parity assertions, and unversioned or invalid output fails the suite.

Written by the indexing model from the issue text.