chasey-dev/immortalwrt-mt798x-rebase — reverse-engineered prompt

Build me a custom ImmortalWrt source tree for MediaTek MT798x routers. I want it based on ImmortalWrt 25.12.4, with the MediaTek OpenWrt feed changes merged in cleanly, so I can compile usable firmware images for supported MT798x devices without manually chasing patches. Please keep the normal OpenWrt style build flow, including feeds, default configs, targets, packages, toolchain, and scripts, and make sure the tree is organized like a real firmware repo that can be built with make.

Also include the MT798x related hardware NAT work from the referenced sources, but be honest in the docs that external device HNAT support is still basic and not fully tested. Note that rxppd should stay in the bridge when using that feature, and mention what works for external WAN or LAN. Add a short README that explains what this repo is, the upstream revisions it is based on, and the basic steps to update feeds and start a build. Look up current docs online if you need to.