feat(contract-validator): add validate_workflow_integration tool (v5.7.1)

Domain Advisory Pattern Hardening - patch release to close gaps from v5.6.0/v5.7.0:

## Added
- New `validate_workflow_integration` MCP tool validates domain plugins expose
  required advisory interfaces (gate command, review command, advisory agent)
- New `MISSING_INTEGRATION` issue type for workflow integration validation
- New `WorkflowIntegrationResult` Pydantic model for structured validation output
- `integrates_with` field on viz-platform and data-platform in marketplace.json
  declaring projman integration metadata
- 4 new test cases for workflow integration validation

## Fixed
- scripts/setup.sh banner version updated from v5.1.0 to v5.7.1

## Documentation
- Updated mcp-tools-reference.md with new tool
- Updated validation-rules.md with Workflow Integration Checks section
- Added /design-gate, /design-review, /data-gate, /data-review to COMMANDS-CHEATSHEET
- Added contract-validator to CONFIGURATION.md plugin table
- Updated README.md Contract Validator tools table

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/contract-validator/commands/validate-contracts.md

@@ -30,6 +30,7 @@
    - Use `validate_compatibility` for pairwise checks
    - Use `validate_agent_refs` for CLAUDE.md agents
    - Use `validate_data_flow` for data sequences
+   - Use `validate_workflow_integration` for domain plugin advisory interfaces
 
 5. **Generate report**:
    - Use `generate_compatibility_report` for full report