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>

markitect/assets/__init__.py

@@ -0,0 +1,72 @@
+"""
+Asset management module for MarkiTect.
+
+This module provides comprehensive asset management capabilities including:
+- Content-addressable asset storage with deduplication
+- JSON-based asset registry and metadata management
+- Cross-platform symlink support with Windows fallback
+- ZIP-based .mdpkg package creation and extraction
+- High-level API for coordinating all asset operations
+
+The module follows the Content-Addressable Package System with Symlinks approach,
+providing efficient storage, deduplication, and cross-platform compatibility.
+
+Key Classes:
+    AssetManager: High-level API coordinator for all asset operations
+    AssetRegistry: JSON-based asset metadata persistence and hashing
+    AssetDeduplicator: Content-based deduplication with symlink support
+    MarkdownPackager: .mdpkg package creation and extraction
+
+Usage:
+    from markitect.assets import AssetManager
+
+    # Initialize asset manager
+    manager = AssetManager()
+
+    # Add an asset
+    result = manager.add_asset(Path("image.png"), "Project logo")
+
+    # Create a package
+    manager.create_package(Path("project/"), Path("project.mdpkg"))
+
+    # Extract a package
+    manager.extract_package(Path("project.mdpkg"), Path("workspace/"))
+"""
+
+from .manager import AssetManager
+from .registry import AssetRegistry
+from .deduplicator import AssetDeduplicator
+from .packager import MarkdownPackager
+from .exceptions import (
+    AssetError, RegistryError, DeduplicationError,
+    PackagingError, AssetManagerError
+)
+from .constants import (
+    DEFAULT_CONFIG, PACKAGE_EXTENSION, MANIFEST_FORMAT_VERSION,
+    DEFAULT_EXCLUDE_PATTERNS, CONFLICT_RESOLUTION_OPTIONS
+)
+
+__version__ = "1.0.0"
+
+# Public API exports
+__all__ = [
+    # Main classes
+    'AssetManager',
+    'AssetRegistry',
+    'AssetDeduplicator',
+    'MarkdownPackager',
+
+    # Exceptions
+    'AssetError',
+    'RegistryError',
+    'DeduplicationError',
+    'PackagingError',
+    'AssetManagerError',
+
+    # Constants
+    'DEFAULT_CONFIG',
+    'PACKAGE_EXTENSION',
+    'MANIFEST_FORMAT_VERSION',
+    'DEFAULT_EXCLUDE_PATTERNS',
+    'CONFLICT_RESOLUTION_OPTIONS'
+]