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_138_markdown_parsing.py

@@ -50,13 +50,14 @@ Detailed content here.
 
         try:
             # This should fail initially (RED phase)
-            structure = parse_markdown_structure(temp_file)
+            structure, front_matter = parse_markdown_structure(temp_file)
 
             # Verify structure
             assert len(structure) == 1  # One part
             assert structure[0].level == 1
             assert structure[0].title == "Part 1: Introduction"
             assert len(structure[0].children) == 2  # Two chapters
+            assert front_matter is None  # No front matter in this test
 
             # Check chapters
             assert structure[0].children[0].level == 2
@@ -154,12 +155,14 @@ Section content.
 
         try:
             # This should fail initially (RED phase)
-            structure = parse_markdown_structure(temp_file)
+            structure, front_matter = parse_markdown_structure(temp_file)
 
-            # Front matter should be handled appropriately
+            # Front matter should be extracted and structure parsed
             assert len(structure) == 1
             assert structure[0].title == "Chapter 1"
             assert structure[0].level == 1
+            assert front_matter is not None
+            assert 'title: "My Document"' in front_matter
 
         finally:
             temp_file.unlink()
@@ -178,10 +181,11 @@ Some more content.
 
         try:
             # This should fail initially (RED phase)
-            structure = parse_markdown_structure(temp_file)
+            structure, front_matter = parse_markdown_structure(temp_file)
 
             # Should return empty structure or handle gracefully
-            assert structure == [] or structure is None
+            assert structure == []
+            assert front_matter is None
 
         finally:
             temp_file.unlink()
@@ -204,10 +208,11 @@ Back to level 2.
 
         try:
             # This should fail initially (RED phase)
-            structure = parse_markdown_structure(temp_file)
+            structure, front_matter = parse_markdown_structure(temp_file)
 
             # Should handle inconsistent levels gracefully
             assert len(structure) == 1  # Main title
+            assert front_matter is None
             assert structure[0].level == 1
             assert len(structure[0].children) >= 1  # Should have children