docs: add contract-validator initial-setup and update version tags

- Add /initial-setup command for contract-validator plugin
- Add contract-validator section to README.md (NEW in v5.0.0)
- Update data-platform version tag: *NEW* -> *NEW in v4.0.0*
- Update viz-platform version tag: *NEW* -> *NEW in v4.0.0*
- Add Contract Validator MCP Server section to README.md
- Add contract-validator to test commands table and repo structure

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

plugins/contract-validator/README.md

@@ -40,6 +40,7 @@ pip install -r requirements.txt
 
 | Command | Description |
 |---------|-------------|
+| `/initial-setup` | Interactive setup wizard |
 | `/validate-contracts` | Full marketplace compatibility validation |
 | `/check-agent` | Validate single agent definition |
 | `/list-interfaces` | Show all plugin interfaces |