[BUG] npm update/install doesn't remove old binary - /usr/local/bin/claude shadows newer version

Bug Description

When updating Claude Code via npm, old binaries at /usr/local/bin/claude are not removed and shadow the newer npm-installed version, causing authentication failures and version confusion.

Environment

• OS: Linux (Ubuntu)
• Old version: 1.0.126 at /usr/local/bin/claude
• New version: 2.1.72 at /usr/bin/claude (npm global)
• npm global root: /usr/lib/node_modules

Reproduction Steps

1. Have old Claude Code installation at /usr/local/bin/claude (version 1.0.126)
2. Run sudo npm install -g @anthropic-ai/claude-code@latest
3. New version installs to /usr/bin/claude via symlink
4. Run claude --version - shows 1.0.126 (old binary in PATH takes precedence)
5. Authentication fails with 401 errors

Expected Behavior

• npm install/update should detect and remove/warn about old binaries
• Or installation should prioritize /usr/local/bin to override old versions
• At minimum, warn users if multiple claude binaries exist

Actual Behavior

• Old binary remains and shadows new installation
• which claude returns /usr/local/bin/claude (old version)
• Users get authentication errors because old version doesn't support new auth flow
• claude --version misleadingly shows old version

Workaround

# Find all claude installations
which -a claude

# Remove old binary
sudo rm /usr/local/bin/claude

# Verify correct version
claude --version  # Now shows 2.1.72

System Info

$ which -a claude
/usr/local/bin/claude  # OLD (1.0.126)
/usr/bin/claude        # NEW (symlink to npm global)
/bin/claude            # NEW (symlink to npm global)

$ ls -la /usr/bin/claude
lrwxrwxrwx 1 root root 52 Mar 11 16:07 /usr/bin/claude -> ../lib/node_modules/@anthropic-ai/claude-code/cli.js

Suggested Fix

Add post-install script to:

1. Check for old binaries in common locations (/usr/local/bin, etc.)
2. Warn or prompt user to remove old installations
3. Or create symlink at /usr/local/bin/claude pointing to npm global version