Implements new `openspec spec` command with three subcommands:
- `spec show`: Display specs with JSON output and filtering options
- `spec list`: List all available specifications
- `spec validate`: Validate spec structure with detailed reporting
Key features:
- JSON output for CI/CD integration (--json flag)
- Content filtering (--requirements, --no-scenarios, -r)
- Strict validation mode (--strict)
- Support for both Overview/Purpose and Requirements/Behavior sections
This enables programmatic access to OpenSpec specifications for external
tools and automated pipelines as specified in the add-spec-commands change.
- Add Zod schemas for specs, changes, requirements, and scenarios
- Implement markdown parser for extracting structured data
- Create validation infrastructure with error/warning/info levels
- Enhance archive command with pre-archive validation
- Add --no-validate flag with confirmation prompt for emergencies
- Enhance diff command with non-blocking validation warnings
- Add JSON converters for spec and change formats
- Add comprehensive test coverage for all validation components
- Fix empty line filtering to preserve formatting in diffs
- Replace prompts with @inquirer/prompts for consistency
- Extract magic strings as constants
- Mark tests as incomplete in tasks.md