Implement --follow mode for live trace watching

[rajfirke]

Description

looprelay play --follow <file> should watch for new lines appended to a trace file using fsnotify and auto-advance to the latest iteration in the TUI.

Implementation

• Add --follow flag to play command
• Use fsnotify to watch the trace file for changes
• Re-parse appended lines and update the player model
• Show a "LIVE" indicator in the status bar
• fsnotify is already a dependency

Location

• internal/cli/play.go
• internal/player/model.go