Skip cross-architecture emulation — use a remote amd64 builder instead

Building amd64 Docker images on an M1 Mac means running every instruction through QEMU emulation, which can make builds 5–10x slower. Instead of burning local CPU cycles on cross-architecture emulation, spin up a cheap Hetzner amd64 server and register it as a remote Docker Buildx builder. Your Mac sends the build context over the network, the remote machine compiles natively at full speed, and you get the image back — no emulation overhead, no fan noise, no waiting.