feat: Add tree tool to generate hierarchical directory structures

[tomholford]

This PR adds a new tree tool that generates a hierarchical JSON representation of directory structures. It provides both human-readable output and AI-friendly structured data that can be analyzed and traversed programmatically.

Implementation Details

• Added a FileNode struct to represent nodes in the directory tree
• Implemented a recursive buildTree method that traverses directories
• Added configurability through optional parameters:
  • depth: Controls traversal depth (default: 3)
  • follow_symlinks: Controls symlink handling (default: false)
• Each node includes rich metadata (path, size, type, modification time)
• Security measures:
  • Respects allowed directory boundaries
  • Validates symlink targets before following
  • Skips problematic files instead of failing
• Returns results as formatted JSON via both text content and embedded resource

User Experience

Example usage:

Claude: Show me the structure of my /projects directory with a depth of 2.
MCP: [Calls tree tool with path="/projects", depth=2]

The tool returns a structured JSON representation that both:

1. Shows in the conversation as formatted text
2. Is available as an embedded resource for programmatic use

Documentation

Updated the README.md to include:

• New tool capabilities in the feature list
• Detailed documentation for the tree tool
• Parameter descriptions and default values