Add `--global` option to `claude install` for system-wide installation

Problem

Currently, claude install only installs to ~/.local/bin/claude (per-user). There's no option for system-wide installation (/usr/local/bin), which is problematic for:

• Multi-user workstations
• Managed environments (sysadmins deploying to multiple machines)
• Standard Linux packaging expectations

Requested Feature

Add a --global flag:

sudo claude install --global   # installs to /usr/local/bin

Or better: provide an official apt repository/deb package.

Current Workaround

Manual copy after install:

sudo cp ~/.local/bin/claude /usr/local/bin/

This breaks automatic updates and isn't documented.