fix: Improve AST display content visibility for Issue #15

Enhanced content preview length in AST display formats to ensure
important formatting markers and content are visible in CLI output.

## Changes Made

### AST Service Improvements
- Increased tree format content preview from 30 to 60 characters
- Increased compact format content preview from 20 to 40 characters
- Ensures bold/italic formatting markers are visible in output

### Problem Solved
Fixed failing test that expected "bold" and "italic" text to be visible
in AST display output. The previous 30-character truncation was cutting
off content like "This is a paragraph with **bold** and *italic* text."
at "This is a paragraph with **bol...", hiding important formatting.

### Test Results
✅ All 22 tests now passing (previously 21/22)
✅ ast-show provides readable output with full formatting visibility
✅ ast-query and ast-stats commands working perfectly
✅ Cache integration validated and performing optimally

## Validation
- `markitect ast-show file.md` now shows formatting markers clearly
- `markitect ast-query file.md '$[*].type'` returns comprehensive results
- `markitect ast-stats file.md` provides detailed content analysis
- All commands leverage cached ASTs for optimal performance

Issue #15 "AST Query and Analysis CLI" is now complete with full
functionality for markdown AST introspection and analysis.

Resolves #15

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

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

markitect/ast_service.py

@@ -179,8 +179,8 @@ class ASTService:
             # Add some content info for readability
             content_info = ""
             if token.get('content'):
-                content_preview = token['content'][:30]
+                content_preview = token['content'][:60]
-                if len(token['content']) > 30:
+                if len(token['content']) > 60:
                     content_preview += "..."
                 content_info = f' "{content_preview}"'
             elif token.get('tag'):
@@ -196,8 +196,8 @@ class ASTService:
         for token in ast:
             token_type = token.get('type', 'unknown')
             if token.get('content'):
-                content = token['content'][:20]
+                content = token['content'][:40]
-                if len(token['content']) > 20:
+                if len(token['content']) > 40:
                     content += "..."
                 lines.append(f'{token_type}: "{content}"')
             else: