Trim package-manager doctor hints

[cbusillo]

Summary

• remove stale npm/Bun/Homebrew-specific uninstall advice from the doctor command
• replace it with source-neutral PATH guidance and current version: 0.6.106
  latest version: v0.6.106
  channel: stable
  published at: 2026-05-26T03:34:10Z
  commit: 9ac61b3
  target: aarch64-apple-darwin
  asset: code-aarch64-apple-darwin.tar.gz
  url: https://github.com/cbusillo/code/releases/download/v0.6.106/code-aarch64-apple-darwin.tar.gz
  sha256: 8bdcb5ce861ca3ef59ea25964c80d3420b6dced49d8f9eb0afebacc9574afb49
  size: 21271957 bytes
  status: up to date
• keep version/path diagnostics intact while avoiding package-manager cleanup recipes

Validation

• git diff --check
• rg -n "bun remove -g|npm uninstall -g|brew uninstall code|npm root -g|npm prefix -g|Prefer using 'coder'" code-rs/cli/src/main.rs
• ./build-fast.sh

Refs #130