feat: add multi-schema validation with numbered selection

Enhanced schema-list and schema-validate commands to support efficient
batch validation of multiple schemas, especially useful when the
metaschema changes.

**schema-list enhancements:**
- Added numbered references (#1, #2, etc.) to all output formats
- Simple format: [1] prefix for each schema
- Table format: # column as first column
- JSON/YAML: number field added to each schema

**schema-validate enhancements:**
- Number selection: `markitect schema-validate 1`
- Range selection: `markitect schema-validate 1-3`
- List selection: `markitect schema-validate 1,3,5`
- Batch validation: `markitect schema-validate --all`
- Filename selection: `markitect schema-validate schema.md`
- Filesystem path: `markitect schema-validate ./schema.md`
- Batch results displayed as clear summary table
- Registry schemas take precedence with filesystem fallback
- Full backward compatibility maintained

**Implementation details:**
- Added ValidationResult dataclass for structured results
- Added helper functions: parse_schema_selector, resolve_schema_source,
  is_filesystem_path, format_validation_summary
- Changed schema_selector from Path to str for flexible input
- Added --all flag for validating all registered schemas
- Comprehensive error handling and helpful usage messages

**Testing:**
- All selection methods tested and working
- Backward compatibility verified
- Parsing utilities tested with unit tests

Completes Phase 5 of Schema-of-Schemas implementation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

CHANGELOG.md

@@ -14,10 +14,23 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - Schema catalog (`markitect/schemas/schema-catalog.yaml`) for metadata and discovery
   - Terminology validation example (`examples/terminology/`) demonstrating schema usage beyond manpages
   - Schema-for-schemas workplan in `roadmap/schema-of-schemas/` directory
-- **Enhanced schema-list Command**: Now displays creation timestamps in all output formats
+- **Enhanced schema-list Command**: Now displays numbered references in all output formats for easy selection
+  - Simple format: `[1] schema-name.md` prefix for each schema
+  - Table format: `#` column as first column
+  - JSON/YAML: `number` field added to each schema
   - Default format shows timestamps inline: `schema-name.json (added: 2026-01-04T23:01:19)`
   - Table format includes Created/Updated columns
   - Cleaner timestamp formatting (removed microseconds)
+- **Multi-Schema Validation**: Enhanced schema-validate command with multiple selection methods
+  - Number selection: `markitect schema-validate 1` validates schema #1
+  - Range selection: `markitect schema-validate 1-3` validates schemas #1-3
+  - List selection: `markitect schema-validate 1,3,5` validates schemas #1,3,5
+  - Batch validation: `markitect schema-validate --all` validates all registered schemas
+  - Filename selection: `markitect schema-validate schema.md` from registry
+  - Filesystem path: `markitect schema-validate ./schema.md` from disk
+  - Batch results displayed as clear summary table with validation status
+  - Registry schemas take precedence over filesystem (with fallback)
+  - Full backward compatibility with existing single-file validation
 - Enhanced control panel UI with better resize handle positioning for improved user interaction
 
 ### Changed
@@ -35,13 +48,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **BREAKING**: Legacy DocumentControls component from TestDrive JSUI plugin system - all control panel functionality now provided by enhanced control panels (ContentsControl, StatusControl, DebugControl, EditControl) with Reset All button functionality moved to EditControl for better maintainability and elimination of code duplication
 
 ### In Progress
-- **Schema-of-Schemas Implementation** (Phase 4 of 6 - Completed ✅)
+- **Schema-of-Schemas Implementation** (Phase 5 of 6 - Completed ✅)
   - ✅ Phase 1: Filename validation for schema naming convention (`markitect/schema_naming.py`, 50 tests)
   - ✅ Phase 2: Markdown schema loader to parse `.md` schema files (`markitect/schema_loader.py`, 35 tests)
   - ✅ Phase 3: Schema-for-schemas metaschema for schema validation (`schema-schema-v1.0.md`, 12 tests)
   - ✅ Phase 4: Migration of 5 existing schemas to new format (migrated 2, deleted 3 duplicates)
-  - ⏳ Phase 5: CLI updates and documentation
-  - ⏳ Phase 6: Integration testing and validation
+  - ✅ Phase 5: CLI enhancements - numbered schema-list, multi-schema validation with selection methods
+  - ⏳ Phase 6: Integration testing and final documentation
 
 ## [0.9.0] - 2025-11-14