feat: Add tool annotations for improved LLM tool understanding

[bryankthompson]

Summary

Adds MCP tool annotations (readOnlyHint, destructiveHint, title) to all 14 tools to help LLMs better understand tool behavior and make safer decisions about tool execution.

Changes

Read-only tools (readOnlyHint: true) - 8 tools:

• read_file - Read file contents
• list_directory - List directory contents
• search_files - Search file names
• get_file_info - Get file metadata
• list_allowed_directories - List allowed directories
• read_multiple_files - Read multiple files
• tree - Directory structure
• search_within_files - Search file contents

Destructive tools (destructiveHint: true) - 6 tools:

• write_file - Create/overwrite files
• create_directory - Create directories
• copy_file - Copy files (creates new)
• move_file - Move/rename files
• delete_file - Delete files
• modify_file - Modify file contents

Why This Matters

• Annotations provide semantic metadata that helps LLMs understand tool behavior
• LLMs can make better decisions about when to use tools and in what order
• Enables safer tool execution by distinguishing read-only from destructive operations
• MCP clients like Claude Code can auto-approve read-only tools while prompting for destructive ones

Testing

• Server builds successfully (go build ./...)
• All tests pass (go test ./...)
• Live verification: Started server and confirmed tools/list returns annotations
• Annotation values match actual tool behavior (read-only vs destructive)

Before/After

Before:

s.AddTool(mcp.NewTool(
    "read_file",
    mcp.WithDescription("Read the complete contents of a file from the file system."),
    mcp.WithString("path", ...),
), h.HandleReadFile)

After:

s.AddTool(mcp.NewTool(
    "read_file",
    mcp.WithDescription("Read the complete contents of a file from the file system."),
    mcp.WithTitleAnnotation("Read File"),
    mcp.WithReadOnlyHintAnnotation(true),
    mcp.WithString("path", ...),
), h.HandleReadFile)