feat: add minui, nextui and myminui platforms

minarch hands every core SDCARD_PATH/Bios/<TAG> as its system directory
and opens no file in it. The scrapers read each pak's launch.sh (core,
tag, devices), each device's core makefile (the project a library is
built from: MyMinUI's dosbox_libretro.so is dosbox-pure) and the minarch
statement, at a pinned commit. The installer recognises the card from
.system/version.txt and refuses a folder inside it.

.github/ISSUE_TEMPLATE/missing-bios.yml

@@ -44,6 +44,9 @@ body:
         - ROCKNIX
         - BizHawk
         - MiSTer FPGA
+        - MinUI
+        - NextUI
+        - MyMinUI
         - Other
     validations:
       required: true