Support "copy pane id" shortcut

This is very useful for coding agents, e.g. 
> Connect to pane `%12` using tmux and analyze my vps error logs

One caveat is that clipboard is different on linux and mac

macOS:
```bash
bind I run-shell "tmux display-message -p '#{pane_id}' | pbcopy"
```

omarchy linux
```bash
bind I run-shell "tmux display-message -p '#{pane_id}' | wl-copy"
```