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>

tests/fixtures/content_test_files/complete_document.md

@@ -0,0 +1,43 @@
+---
+title: "Complete Test Document"
+author: "Test Author"
+date: 2025-10-02
+tags: ["test", "markdown", "matters"]
+---
+
+# Complete Test Document
+
+This is the main content of the document. It contains multiple paragraphs and various elements to test content extraction.
+
+Author: John Doe
+Project: MarkdownMatters Implementation
+Status: In Progress
+
+## Section 1
+
+Here is some content in the first section. This paragraph contains exactly twenty-five words to help with word counting tests.
+
+## Section 2
+
+Another section with different content. This helps test paragraph counting and ensures that the content parser works correctly across multiple sections.
+
+The final paragraph of the main content area.
+
+---
+
+```yaml tailmatter
+qa_checklist:
+  - requirement: "All headers verified"
+    complete: true
+  - requirement: "Links checked"
+    complete: false
+
+editorial:
+  status: "In Review"
+  reviewer: "jane.doe"
+  version: 1.2
+
+agent_config:
+  role: "documentation_reviewer"
+  access_scope: "content"
+```

tests/fixtures/content_test_files/contentmatter_inline.md

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+# Document with Contentmatter
+
+This document contains MultiMarkdown key-value pairs within the content body.
+
+Author: Jane Smith
+Project: Content Testing
+Keywords: markdown, contentmatter, testing
+
+## Introduction
+
+This section demonstrates contentmatter usage. The key-value pairs above are part of the content but provide metadata.
+
+Reference: https://example.com/docs
+Version: 2.1
+License: MIT
+
+The content continues here with more text for testing purposes. This paragraph helps verify that contentmatter is preserved in content extraction.
+
+## Conclusion
+
+Final section with summary content. Word counting should include the contentmatter lines as part of the content.

tests/fixtures/content_test_files/frontmatter_only.md

@@ -0,0 +1,15 @@
+---
+title: "Frontmatter Only Document"
+author: "Test Author"
+date: 2025-10-02
+---
+
+# Frontmatter Only Document
+
+This document only has frontmatter, no tailmatter. The content should be extracted without the frontmatter block.
+
+This is a simple paragraph for testing. It has exactly twelve words for counting purposes.
+
+## Simple Section
+
+Another paragraph here. This helps test the content extraction when only frontmatter is present.

tests/fixtures/content_test_files/plain_markdown.md

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+# Plain Markdown Document
+
+This is a simple markdown document without any frontmatter or tailmatter. Just pure content.
+
+This paragraph contains exactly fifteen words for testing the word counting functionality of the parser.
+
+## Section One
+
+Another section with regular content. This helps test the basic content extraction without any matter zones.
+
+## Section Two
+
+The final section with some more content. Multiple paragraphs help test paragraph counting and line counting features.

tests/fixtures/content_test_files/tailmatter_only.md

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+# Tailmatter Only Document
+
+This document only has tailmatter, no frontmatter. The content should be extracted without the tailmatter block.
+
+This is a test paragraph. It contains exactly ten words for counting purposes.
+
+Another paragraph for testing content extraction with tailmatter present but no frontmatter.
+
+---
+
+```yaml tailmatter
+qa_checklist:
+  - requirement: "Document structure validated"
+    complete: true
+
+editorial:
+  status: "Draft"
+  reviewer: "test.reviewer"
+```