fix: waiter Ctrl+C not responding in interactive mode

rawmode_linux.go only cleared ICANON|ECHO but left ISIG enabled,
so the terminal driver caught Ctrl+C and generated SIGINT.
signal.Notify caught the SIGINT but no goroutine consumed the
channel, effectively swallowing the signal.

Fix: also clear ISIG so Ctrl+C is delivered as byte 0x03,
which the line editor handles with os.Exit(130). Also set
VMIN=1, VTIME=0 for proper blocking read behavior.

cmd/waiter/rawmode_defs.go

@@ -15,4 +15,7 @@ const (
 	TCSETS = 0x5402
 	ICANON = 0x2
 	ECHO   = 0x8
+	ISIG   = 0x1
+	VMIN   = 6
+	VTIME  = 5
 )

cmd/waiter/rawmode_linux.go

@@ -13,7 +13,9 @@ func setRawMode(fd int) (func(), error) {
 		return func() {}, err
 	}
 	new := old
-	new.Lflag &^= ICANON | ECHO
+	new.Lflag &^= ICANON | ECHO | ISIG
+	new.Cc[VMIN] = 1
+	new.Cc[VTIME] = 0
 	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), TCSETS, uintptr(unsafe.Pointer(&new))); err != 0 {
 		return func() {}, err
 	}