fix: iris stops working after exec a command in bash (#66)

Fix #65

when the user presses Enter to run a command, Iris sets `isCommandActive
= true` so it knows a command is running and skips rendering the
overlay. After the command finishes, `isCommandActive` needs to reset to
`false` for Iris to work again. In zsh/fish, preexec/precmd hooks send
an `IRIS_CMD_STOP` signal over the IPC pipe, which Iris receives to
reset `isCommandActive = false`. Bash has no equivalent hook, so
`IRIS_CMD_STOP` is never sent and `isCommandActive` stays stuck at true
forever

so I added a bash-only fallback inside `isExecuting()`: if
`isCommandActive` is true but `TIOCGPGRP` (a kernel API) confirms the
shell's process group is back in the foreground (meaning the command
finished), automatically reset `isCommandActive` to false. zsh/fish
still rely on IPC signals as before

also added a `PROMPT_COMMAND` hook to iris init bash to `send
IRIS_CMD_STOP` after every command (belt-and-suspenders), though that's
not the main fix

root/wrapper.go

@@ -287,6 +287,14 @@ func runWrapper() {
 	renderOverlay := func() {}
 	isExecuting := func() bool {
 		if isCommandActive.Load() {
+			// for bash: no preexec/precmd hooks, so fall back to TIOCGPGRP to detect when shell returns
+			if shellName == "bash" {
+				pgrp, pgrpErr := unix.IoctlGetInt(int(ptmx.Fd()), unix.TIOCGPGRP)
+				if pgrpErr == nil && pgrp == shellPGID {
+					isCommandActive.Store(false)
+					return false
+				}
+			}
 			return true
 		}
 		pgrp, err := unix.IoctlGetInt(int(ptmx.Fd()), unix.TIOCGPGRP)