FINALLY FIXED!!!!!!!!!
Unable to budge the slide handle, I finally resorted to the tried and true principal my father once warned me against, but which has nevertheless worked with a little common sense.
I forced it. I put on the heaviest sole shoe I had at hand, put it on, placed the butt against the floor and, using my foot, forced it to cock. It took three monumental tries, but it finally opened, and then, *PLANK* — it snapped back. I then grabbed the slide handle and pulled it back and this time it went smoothly, without any problem whatsover. I snapped the safety off and pulled the trigger and it went click, then I popped the magazine in and it works like a charm.
Thanks to everyone for their patience and suggestions. I never got around to putting that recoil buffer back in, but who cares? If the thing ever gets dirty enough that it needs disassembling, I'm just going to fold the stock, take out the magazine, lock the slide back and put it in the dish washer!