Job status tracking and notification

[cdprice02]

Maintain a job table in ShellCtx that tracks all background jobs.

Job table should store:

• Job number
• PID
• Status (Running, Stopped, Done)
• Original command string

Behavior:

• jobs displays the job table
• When a background job completes, notify user before next prompt: [1]+ Done sleep 5
• Use waitpid with WNOHANG to poll without blocking

Acceptance criteria:

• Job table tracks background jobs
• jobs displays correct status
• Completion notifications appear at prompt
• No blocking on job status checks