Any chance that there is a self-timer button right behind the shutter cocking lever? There's a chance that the button was to the rear and the lever was able to travel further than usual and engage the self-timer, which are notorious for jamming in old shutters. Hard to tell in the photo.
Fire the shutter (meaning press the release button) and apply pressure to the cocking/tensioning lever to get it to return to its rest position. Keep pressure on for a while. You might have the self-timer activated and you'll need to get through that mechanism and then the slow speed escapement.
Also turn the speed dial to 1/25 or 1/50- this disengages the slow speed escapement and will make it more likely that it will return.
A few drops of naphtha into the lever slot would be worth a try. Drops! Small ones!
All of this is to get you going, not to do it right. See what happens. Disassembly and cleaning is the 'right' answer but that may not be needed for now.