BirdDog PLAY Patcher

A BirdDog PLAY is an NDI decoder with no way in from outside the room it is sitting in. This builds an installable firmware package that adds one: an SSH key, Tailscale, and an NDI KVM endpoint that turns the keyboard and mouse on the PLAY's USB port into control of whatever machine it is displaying. The surprise is that it needs nothing from you but a public key — the stock updater runs a script from the uploaded archive as root with no signature check, so a valid package is an ordinary gzip'd tar and there is nothing to decrypt. That means no upload, no vendor keys, and the whole thing assembles in the browser: tar, gzip and SHA-256 are native APIs now. The installer is readable bash that refuses to run on the wrong hardware, stays off the recovery path, and cannot reach the kernel or bootloader. Confirmed on a real unit — Tailscale carries 195 Mbps over userspace networking, and the KVM agent drove a Windows machine using only the free NDI SDK.