At least the VLAN 100 should not apply anymore (I removed it from the GS108T v3 wiki entry). The device should configure itself to 192.168.1.1 with untagged VLAN just like any other OpenWrt device.
The LEDs dying on you are normal unfortunately, there is code around somewhere to drive these but it's not upstream or in OpenWrt yet AFAIK.
Set your client to a static 192.168.1.100, then try pinging or SSH'ing into 192.168.1.1. FWIW, if you get access to the device again (you might need to open it up and tinker some with the serial - I managed to get it going without soldering, but you need a steady hand), you can use 22.03 pre-release images. Those come with a web UI by default and you can easily upgrade to stable releases later on; there's not much surplus value (if any) in running master builds on your specific device at this point.
Great! I'd downgrade to a 22.03 pre-release image, you can scp that over to /tmp, verify the checksum and then use sysupgrade -n $path_to_file. The -n is important, since it would be like you'd flash a new image from OEM cleanly. Without it you'd be preserving settings and master settings are only forward, not backward compatible (in case anything already changed between 22.03 getting branched and master progressing).