containerize and add basic setup to backend

backend/Dockerfile

@@ -0,0 +1,13 @@
+FROM golang:1.24-alpine AS build
+
+WORKDIR /app
+
+COPY . .
+RUN go build -o nuchat fergus.molloy.xyz/nuchat
+
+FROM scratch
+WORKDIR /app
+
+COPY --from=build /app/nuchat .
+
+ENTRYPOINT ["/app/nuchat"]