feat: Implement Issue #56 - Data-driven multiple draft generation

Add generate-drafts CLI command for batch document generation from data sources.
Supports JSON and CSV data with field mapping, validation, and automatic file naming.

Features:
- CLI command: markitect generate-drafts <schema> <data> -o <output_dir>
- JSON and CSV data source support
- Field mapping via x-markitect-field-mapping schema extensions
- Template variable substitution (e.g., {name} -> actual values)
- Data validation with required field checking
- Automatic file naming based on data content
- Schema reference metadata in generated files
- Integration with existing stub generation (Issue #55)

Technical implementation:
- New DraftGenerator class with comprehensive data processing
- Enhanced CLI with generate-drafts command and error handling
- Comprehensive test suite with 11 test cases covering all acceptance criteria
- Field mapping extraction and validation
- Template content substitution for data-driven content

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

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

markitect/cli.py

@@ -2061,6 +2061,81 @@ def generate_stub(config, schema_file, output, style, title):
         sys.exit(1)
 
 
+@cli.command('generate-drafts')
+@click.argument('schema_file', type=click.Path(exists=True, path_type=Path))
+@click.argument('data_source', type=click.Path(exists=True, path_type=Path))
+@click.option('--output-dir', '-o', type=click.Path(path_type=Path), required=True,
+              help='Output directory for generated drafts')
+@pass_config
+def generate_drafts(config, schema_file, data_source, output_dir):
+    """
+    Generate multiple document drafts from a schema and data source.
+
+    Creates multiple markdown documents by combining a JSON schema template
+    with data from JSON or CSV sources. Each record in the data source
+    generates a separate draft file with field mapping applied.
+
+    SCHEMA_FILE: Path to the JSON schema file
+    DATA_SOURCE: Path to JSON or CSV data source file
+
+    Examples:
+        markitect generate-drafts schema.json data.json -o ./drafts/
+        markitect generate-drafts blog_schema.json posts.csv -o ./blog_posts/
+
+    Field Mapping:
+        Use x-markitect-field-mapping extension in schema to map data fields
+        to content areas. Data validation ensures compatibility.
+
+    Output:
+        Generated drafts maintain schema references for validation and
+        use automatic file naming based on data content.
+    """
+    try:
+        if config.get('verbose'):
+            click.echo(f"Generating drafts from schema: {schema_file}", err=True)
+            click.echo(f"Using data source: {data_source}", err=True)
+            click.echo(f"Output directory: {output_dir}", err=True)
+
+        from .draft_generator import DraftGenerator
+
+        generator = DraftGenerator()
+
+        # Load schema
+        import json
+        with open(schema_file, 'r') as f:
+            schema = json.load(f)
+
+        # Generate drafts
+        generated_files = generator.generate_drafts_from_data_source(
+            schema=schema,
+            data_source=data_source,
+            output_dir=Path(output_dir),
+            schema_file_path=str(schema_file)
+        )
+
+        # Report results
+        click.echo(f"✅ Generated {len(generated_files)} drafts in {output_dir}")
+        if config.get('verbose'):
+            for file_path in generated_files:
+                click.echo(f"  - {file_path}", err=True)
+
+    except FileNotFoundError as e:
+        click.echo(f"Error: {e}", err=True)
+        sys.exit(1)
+    except json.JSONDecodeError as e:
+        click.echo(f"Error: Invalid JSON in schema file - {e}", err=True)
+        sys.exit(1)
+    except ValueError as e:
+        click.echo(f"Error: {e}", err=True)
+        sys.exit(1)
+    except Exception as e:
+        click.echo(f"Draft generation error: {e}", err=True)
+        if config and config.get('verbose'):
+            import traceback
+            click.echo(traceback.format_exc(), err=True)
+        sys.exit(1)
+
+
 @cli.group('associated-files')
 @pass_config
 def associated_files_group(config):