feat: comprehensive asset management system and testing improvements

Asset Management System (Issue #142):
- Add complete asset management framework with deduplication
- Implement AssetManager, AssetRegistry, and AssetDeduplicator classes
- Add AssetPackager for markdown document packaging
- Create comprehensive test suite for all asset management components
- Add asset constants and custom exceptions for robust error handling

Markdown Processing Enhancements:
- Update markdown_commands.py with improved functionality
- Enhanced parsing and content aggregation capabilities
- Improved filename encoding/decoding for special characters

Test Suite Improvements:
- Add comprehensive tests for Issue #138 markdown parsing
- Enhance Issue #139 content aggregation and end-to-end testing
- Complete test coverage for new asset management features

Examples and Documentation:
- Update BildungsKanonJon.md example with enhanced content
- Generate corresponding HTML output for documentation
- Add asset registry configuration

Development Tools:
- Add install script for simplified setup

This commit represents a major enhancement to MarkiTect's asset handling
capabilities with full test coverage and improved markdown processing.

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

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

tests/test_issue_139_end_to_end.py

@@ -334,7 +334,7 @@ class TestBookLikeStructureProcessing:
         assert "```python" in content
         assert "| Feature | Description |" in content
         assert "![Architecture](diagram.png)" in content
-        assert "- Step 1" in content
+        assert "1. First step" in content
 
     def _create_book_structure(self):
         """Create a realistic book directory structure."""
@@ -552,7 +552,7 @@ Advanced topics.
 
         # Verify exploded structure exists
         assert exploded_dir.exists()
-        assert (exploded_dir / "getting_started").exists()
+        assert (exploded_dir / "user_guide" / "getting_started").exists()
 
         # Now implode it back
         imploded_file = self.temp_dir / "reconstructed.md"