fix(core): normalize file paths in read tool output

[scarf005]

Summary

• Show clean relative paths for files inside the worktree
• Show absolute paths for files outside the worktree instead of ugly ../../../../../../ paths

Changes

Modified the read tool to check if a file is within the worktree before deciding how to display the path:

• Inside worktree: Show relative path (e.g., src/tool/read.ts)
• Outside worktree: Show absolute path (e.g., /home/user/other/file.ts)

This improves UX by avoiding confusing paths like read ../../../../../../home/scarf/foo/bar/baz.ts.

Testing

Verified that lsp_diagnostics passes on the modified file.