feat: Complete Issue #38 TDD8 Cycle 1 - Content command family implementation

Implemented comprehensive content command family for MarkdownMatters CLI following TDD8 methodology and MarkdownMatters specification.

## TDD8 Cycle 1 - Content Commands

### Core Implementation
- Content parser for extracting main content without matter zones
- Content statistics calculator (words, lines, paragraphs, characters)
- CLI commands: `content-get` and `content-stats`
- Full integration with existing markitect CLI

### MarkdownMatters Compliance
- Correctly removes YAML/TOML/JSON frontmatter
- Correctly removes tailmatter blocks (`yaml tailmatter`, `json tailmatter`)
- Preserves contentmatter (MultiMarkdown key-value pairs within content)
- Follows three-zone specification from wiki/MarkdownMatters.md

### Module Structure
```
markitect/content/
├── __init__.py          # Module exports
├── parser.py           # ContentParser with matter zone removal
├── stats.py            # ContentStats data class
└── commands.py         # CLI commands implementation
```

### CLI Commands Added
- `markitect content-get --file [path]` - Extract pure content
- `markitect content-stats --file [path]` - Calculate content statistics

### Test Coverage
- 16 comprehensive tests covering all scenarios
- Test fixtures for different document types
- CLI integration tests with Click testing
- Edge case handling (file not found, empty content, etc.)

### Validation Results
- All tests pass (16/16)
- Manual CLI testing confirmed
- Proper matter zone separation validated
- Statistics calculation accuracy verified

## Technical Architecture

### ContentParser Class
- `extract_content()` - Remove frontmatter and tailmatter
- `calculate_stats()` - Generate comprehensive statistics
- `_remove_frontmatter()` - YAML frontmatter removal
- `_remove_tailmatter()` - Tailmatter block removal

### ContentStats Data Class
- word_count, line_count, paragraph_count, character_count
- JSON serialization support via `to_dict()`

## GAMEPLAN Progress
- ✅ TDD8 Cycle 1: Content Commands (COMPLETE)
- 🔄 Next: Cycle 2 - Frontmatter Commands
- Remaining: Contentmatter, Tailmatter command families

This implements the foundation for Issue #38 with 6 remaining cycles planned for complete MarkdownMatters CLI functionality.

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

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

markitect/content/stats.py

@@ -0,0 +1,25 @@
+"""
+Content statistics data structures.
+"""
+
+from dataclasses import dataclass
+from typing import Dict, Any
+
+
+@dataclass
+class ContentStats:
+    """Statistics about markdown content."""
+
+    word_count: int
+    line_count: int
+    paragraph_count: int
+    character_count: int
+
+    def to_dict(self) -> Dict[str, Any]:
+        """Convert stats to dictionary."""
+        return {
+            "word_count": self.word_count,
+            "line_count": self.line_count,
+            "paragraph_count": self.paragraph_count,
+            "character_count": self.character_count
+        }