feat: complete Issue #150 - Advanced Packaging Features (.mdz, .mdt)

Implement comprehensive advanced packaging system using complete TDD8 methodology:

## Core Features Delivered
- **MDZ Format**: Self-contained ZIP packages with embedded assets and metadata
- **Transclusion Engine**: Dynamic content inclusion with variables and conditionals
- **Asset Management**: Automated discovery, integrity validation, and path rewriting
- **Variant Integration**: Seamless integration with existing explode-implode system

## Technical Implementation
- **53 comprehensive tests** with 100% coverage for new functionality
- **Circular import resolution** using lazy loading pattern in variant factory
- **Cross-platform compatibility** with proper path handling
- **Robust error handling** with specialized exception hierarchy

## Quality Assurance
- ✅ All 1798 tests passing (100% system compatibility maintained)
- ✅ Complete documentation (user guide + API reference)
- ✅ Working demonstration script showcasing all features
- ✅ Zero breaking changes to existing functionality

## Files Added/Modified
- **Core Implementation**: 17 new files (4,149+ lines)
- **Documentation**: Complete user and API documentation
- **Tests**: 53 new tests across 3 test modules
- **Integration**: Enhanced variant factory with MDZ support

Built on solid foundation from Issues #148-149. Production-ready with
comprehensive test coverage and full backward compatibility.

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

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

markitect/packaging/transclusion/context.py

@@ -0,0 +1,155 @@
+"""
+Transclusion context management.
+
+Provides context objects that manage variables, paths,
+and state during transclusion processing.
+"""
+
+from pathlib import Path
+from typing import Dict, Any, Optional, Set, List
+
+
+class TransclusionContext:
+    """
+    Context object for transclusion operations.
+
+    Manages variables, paths, processing state, and circular reference
+    detection during transclusion processing.
+    """
+
+    def __init__(self, base_path: Optional[Path] = None,
+                 variables: Optional[Dict[str, Any]] = None,
+                 max_depth: int = 10):
+        """
+        Initialize transclusion context.
+
+        Args:
+            base_path: Base path for relative file resolution
+            variables: Initial variables for substitution
+            max_depth: Maximum inclusion depth to prevent infinite recursion
+        """
+        self.base_path = base_path or Path.cwd()
+        self.variables = variables or {}
+        self.max_depth = max_depth
+        self.current_depth = 0
+        self.inclusion_stack: List[Path] = []
+        self.processed_files: Set[Path] = set()
+
+    def enter_file(self, file_path: Path) -> None:
+        """
+        Enter processing of a file.
+
+        Args:
+            file_path: Path of file being processed
+
+        Raises:
+            CircularReferenceError: If file creates circular reference
+            DepthLimitError: If max depth exceeded
+        """
+        from ..errors import CircularReferenceError, DepthLimitError
+
+        # Check depth limit
+        if self.current_depth >= self.max_depth:
+            raise DepthLimitError(f"Maximum inclusion depth {self.max_depth} exceeded")
+
+        # Check for circular references
+        resolved_path = file_path.resolve()
+        if resolved_path in self.inclusion_stack:
+            cycle_start = self.inclusion_stack.index(resolved_path)
+            cycle = self.inclusion_stack[cycle_start:] + [resolved_path]
+            cycle_str = " -> ".join(str(p) for p in cycle)
+            raise CircularReferenceError(f"Circular reference detected: {cycle_str}")
+
+        # Enter file
+        self.inclusion_stack.append(resolved_path)
+        self.current_depth += 1
+
+    def exit_file(self, file_path: Path) -> None:
+        """
+        Exit processing of a file.
+
+        Args:
+            file_path: Path of file being exited
+        """
+        resolved_path = file_path.resolve()
+        if self.inclusion_stack and self.inclusion_stack[-1] == resolved_path:
+            self.inclusion_stack.pop()
+            self.current_depth -= 1
+            self.processed_files.add(resolved_path)
+
+    def resolve_path(self, path: str) -> Path:
+        """
+        Resolve a path relative to the current base path.
+
+        Args:
+            path: Path to resolve
+
+        Returns:
+            Resolved Path object
+        """
+        path_obj = Path(path)
+        if path_obj.is_absolute():
+            return path_obj
+        else:
+            return self.base_path / path_obj
+
+    def set_variable(self, name: str, value: Any) -> None:
+        """
+        Set a variable in the context.
+
+        Args:
+            name: Variable name
+            value: Variable value
+        """
+        self.variables[name] = value
+
+    def get_variable(self, name: str, default: Any = None) -> Any:
+        """
+        Get a variable from the context.
+
+        Args:
+            name: Variable name
+            default: Default value if variable not found
+
+        Returns:
+            Variable value or default
+        """
+        return self.variables.get(name, default)
+
+    def substitute_variables(self, text: str) -> str:
+        """
+        Substitute variables in text using simple {{variable}} syntax.
+
+        Args:
+            text: Text containing variable references
+
+        Returns:
+            Text with variables substituted
+        """
+        import re
+
+        def replace_var(match):
+            var_name = match.group(1).strip()
+            return str(self.get_variable(var_name, match.group(0)))
+
+        return re.sub(r'\{\{([^}]+)\}\}', replace_var, text)
+
+    def create_child_context(self, new_base_path: Optional[Path] = None) -> 'TransclusionContext':
+        """
+        Create a child context for nested processing.
+
+        Args:
+            new_base_path: New base path for the child context
+
+        Returns:
+            New TransclusionContext with inherited state
+        """
+        child = TransclusionContext(
+            base_path=new_base_path or self.base_path,
+            variables=self.variables.copy(),
+            max_depth=self.max_depth
+        )
+        child.current_depth = self.current_depth
+        child.inclusion_stack = self.inclusion_stack.copy()
+        child.processed_files = self.processed_files.copy()
+        return child