This is the DIY programming header I use, and the reason there is no "programming JIG" yet:


Aliexpress links:
pogo pins: [1] [2] [3]
pin header: [4] (2 mm pitch is a less common item, but I had no space on board for 2.54 mm spacing)
UV curable resin: local model shop, beauty shop or [5]
cables: [6] (female-female both ends; remove plastic socket on one end to fit the pogo pins inside)

An en-mass programming requires the pogo pins. The rest is optional.
I use the UV-curable resin to secure the cables to the transponder as well (put some over the solder joints).

PROGRAMMING
Try tools with GUI, like Stm32CubeProg. Here is a precompiled hex, so you don't have to compile it.
The programming points are labeled on the silkscreen, note "CLK" is "SWCLK" and "DIO" is "SWDIO".

SIMPLEST DECODER SETUP
You can use everything from a single Windows machine (decoder + bridge + zround), no need for Raspberry or thin-client:
https://github.com/zsellera/openstin...ial-windows.md

CLOSING THOUGHTS
I know you have more questions than answers here; I'll answer them later when I have more time. I hope this helps already.