fix: start iris in multiplexer panes instead of inheriting a dead one (#120)

closes #62
when you open a new Zellij pane, the shell inherits Iris’s environment
variables, so it thinks Iris is already running. But the pane doesn't
inherit the underlying connection (FD 13), so suggestions silently fail
into a dead pipe

the old code only checked for `tmux` by process name, ignoring Zellij
completely

- Fixed:

instead of checking for specific app names, Iris now tracks the active
terminal device (`IRIS_TTY`)

if a new shell detects that it's on a different `TTY` than Iris, it
clears the stale environment variables so Iris can start fresh. The
`IRIS_PID != PPID` check prevents Iris from trying to re-exec itself
when spawning sub-shells.

```sh
if [ -n "$IRIS_PID" ] && [ "$IRIS_PID" != "$PPID" ] && [ "${TTY:-$(tty 2>/dev/null)}" != "$IRIS_TTY" ]; then
    unset IRIS_PID IRIS_IS_CHILD IRIS_FD IRIS_TTY
fi

```

root/init.go

@@ -25,10 +25,10 @@ For example, add this to your ~/.zshrc:
 		case "zsh":
 			fmt.Printf(`
 # Iris Autostart Hook
-if [ -n "$TMUX" ] && [ -n "$IRIS_PID" ]; then
-    if ps -o comm= -p $PPID 2>/dev/null | grep -q "tmux"; then
-        unset IRIS_PID IRIS_IS_CHILD IRIS_FD
-    fi
+# a multiplexer pane inherits IRIS_* but runs on its own tty, so those vars
+# point at an iris that is not driving this terminal
+if [ -n "$IRIS_PID" ] && [ "$IRIS_PID" != "$PPID" ] && [ "${TTY:-$(tty 2>/dev/null)}" != "$IRIS_TTY" ]; then
+    unset IRIS_PID IRIS_IS_CHILD IRIS_FD IRIS_TTY
 fi
 
 if [ -z "$IRIS_PID" ] && [ -z "$IRIS_RESCUE" ]; then
@@ -68,10 +68,10 @@ fi
 		case "bash":
 			fmt.Printf(`
 # Iris Autostart Hook
-if [ -n "$TMUX" ] && [ -n "$IRIS_PID" ]; then
-    if ps -o comm= -p $PPID 2>/dev/null | grep -q "tmux"; then
-        unset IRIS_PID IRIS_IS_CHILD IRIS_FD
-    fi
+# a multiplexer pane inherits IRIS_* but runs on its own tty, so those vars
+# point at an iris that is not driving this terminal
+if [ -n "$IRIS_PID" ] && [ "$IRIS_PID" != "$PPID" ] && [ "$(tty 2>/dev/null)" != "$IRIS_TTY" ]; then
+    unset IRIS_PID IRIS_IS_CHILD IRIS_FD IRIS_TTY
 fi
 
 if [ -z "$IRIS_PID" ] && [ -z "$IRIS_RESCUE" ]; then
@@ -96,11 +96,16 @@ fi
 		case "fish":
 			fmt.Printf(`
 # Iris Autostart Hook
-if set -q TMUX; and set -q IRIS_PID
-    if ps -o comm= -p $PPID 2>/dev/null | grep -q "tmux"
+# a multiplexer pane inherits IRIS_* but runs on its own tty, so those vars
+# point at an iris that is not driving this terminal
+if set -q IRIS_PID
+    set -l iris_ppid (ps -o ppid= -p $fish_pid 2>/dev/null | string trim)
+    set -l iris_cur_tty (tty 2>/dev/null)
+    if test "$IRIS_PID" != "$iris_ppid"; and test "$iris_cur_tty" != "$IRIS_TTY"
         set -e IRIS_PID
         set -e IRIS_IS_CHILD
         set -e IRIS_FD
+        set -e IRIS_TTY
     end
 end