feat: implement Phase 4 - Schema Migration

Completed Phase 4 of the schema-of-schemas implementation with successful
migration of all legacy schemas to the new markdown format following the
naming convention.

Migration Script (scripts/migrate_schemas.py - 240 lines):
- Automated schema migration from JSON to markdown format
- Updates version and $id fields to follow conventions
- Generates proper frontmatter metadata
- Dry-run mode for safe testing
- Database cleanup functionality
- Comprehensive progress reporting

Schemas Migrated (2):
- terminology-schema.json → terminology-schema-v1.0.md
  - Fixed missing version field
  - Updated $id from /terminology-v1.json to /terminology/v1.0
  - Validates successfully against metaschema

- api-documentation → api-documentation-schema-v1.0.md
  - Added version: 1.0.0
  - Updated $id to follow /api-documentation/v1.0 format
  - Validates successfully against metaschema

Schemas Deleted (3):
- markdown-manpage (duplicate of manpage-schema-v1.0.md)
- markdown-manpage-schema.json (duplicate of manpage-schema-v1.0.md)
- enhanced-manpage (replaced by manpage-schema-v1.0.md)

CLI Enhancement (markitect/cli.py):
- Updated schema-ingest to support markdown (.md) files
- Auto-detects file type and uses MarkdownSchemaLoader for .md files
- Extracts JSON schema from markdown for database storage
- Maintains backward compatibility with JSON files

Final Schema Registry (4 schemas):
✅ terminology-schema-v1.0.md - Terminology validation
✅ api-documentation-schema-v1.0.md - API documentation structure
✅ manpage-schema-v1.0.md - Unix manual pages
✅ schema-schema-v1.0.md - Metaschema for validating schemas

All schemas:
- Follow naming convention: {domain}-schema-v{major}.{minor}.md
- Include proper frontmatter with schema-id, version, status
- Validate successfully against schema-schema-v1.0.md metaschema
- Stored in database and ready for use

Progress Tracking:
- Updated TODO.md with Phase 4 completion
- Updated CHANGELOG.md with migration details
- Next: Phase 5 - CLI & Documentation Updates

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

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

CHANGELOG.md

@@ -35,11 +35,11 @@ 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 3 of 6 - Completed ✅)
+- **Schema-of-Schemas Implementation** (Phase 4 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 (will remove 2 duplicates)
+  - ✅ 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