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>

markitect/cli.py

@@ -1617,33 +1617,52 @@ def validate(config, file_path, schema, schema_json, quiet, detailed_errors, err
 @pass_config
 def schema_ingest(config, schema_file, name):
     """
-    Read and store a JSON schema file in the database.
+    Read and store a schema file in the database.
 
+    Supports both JSON (.json) and Markdown (.md) schema files.
     Validates schemas against the MarkiTect metaschema to ensure compatibility
     with MarkiTect features like heading text capture and content instructions.
-    Implements Issue #3 and Issue #50 functionality.
 
-    SCHEMA_FILE: Path to the JSON schema file to store
+    SCHEMA_FILE: Path to the schema file to store (.json or .md)
 
     Examples:
         markitect schema-ingest my_schema.json
+        markitect schema-ingest manpage-schema-v1.0.md
         markitect schema-ingest external_schema.json --name custom-name
-        markitect schema-ingest markitect_schema.json -v    # Show metaschema validation
     """
     try:
         # Determine schema name
         schema_name = name if name else schema_file.name
 
-        # Read schema file content
-        with open(schema_file, 'r', encoding='utf-8') as f:
-            schema_content = f.read()
+        # Load schema based on file type
+        if schema_file.suffix == '.md':
+            # Load markdown schema
+            from .schema_loader import MarkdownSchemaLoader
+            loader = MarkdownSchemaLoader()
 
-        # Validate JSON format
-        try:
-            schema_data = json.loads(schema_content)
-        except json.JSONDecodeError as e:
-            click.echo(f"Error: Invalid JSON in schema file - {e}", err=True)
-            sys.exit(1)
+            try:
+                schema_data_full = loader.load_schema(schema_file)
+                schema_data = schema_data_full['schema']
+
+                # Store the JSON content for database
+                schema_content = json.dumps(schema_data, indent=2)
+
+                if config.get('verbose'):
+                    click.echo(f"✅ Loaded markdown schema: {schema_file.name}")
+            except Exception as e:
+                click.echo(f"Error: Failed to load markdown schema - {e}", err=True)
+                sys.exit(1)
+        else:
+            # Load JSON schema
+            with open(schema_file, 'r', encoding='utf-8') as f:
+                schema_content = f.read()
+
+            # Validate JSON format
+            try:
+                schema_data = json.loads(schema_content)
+            except json.JSONDecodeError as e:
+                click.echo(f"Error: Invalid JSON in schema file - {e}", err=True)
+                sys.exit(1)
 
         # Validate against MarkiTect metaschema
         from .metaschema import MetaschemaValidator