[Feature Request] Show PID of blocking process in "claude update" error message

Feature Description

When claude update fails because another process is updating, the error message should include the PID of the blocking process:

Current behavior:

$ claude update
Current version: 2.0.65
Checking for updates...
Another process is currently updating Claude. Please try again in a moment.

Proposed behavior:

$ claude update
Current version: 2.0.65
Checking for updates...
Another process (PID 12345) is currently updating Claude. Please try again in a moment.

Use Case

This helps users:

1. Verify if a legitimate update is in progress vs a stale lock
2. Identify and kill the blocking process if needed (kill 12345)
3. Debug issues when multiple Claude instances are running

Related Issues

• #13085 - VS Code extension causing update conflicts
• #13705 - Stale lock files blocking updates
• #6200 - Update giving "please wait" repeatedly

These are bug reports about the lock mechanism; this request is for improving the error message to aid debugging.

Environment

• Platform: Linux
• Terminal: Console (no VS Code extension)