Add Code Navigation and Investigation Guide for Go LSP Tools

Added a new section to the CLAUDE.md documentation that explains how to use Go Language Server Protocol (LSP) tools when working with the Coder codebase. The guide includes:

• Commands for finding function definitions, symbol references, and getting symbol information
• Examples of LSP usage with specific commands
• Guidance on when to use LSP versus other tools like grep or bash
• A structured investigation strategy for navigating the codebase, starting with route registration and tracing through to implementations

This documentation helps developers more efficiently explore and understand the codebase structure.