add .gitignore and Dockerfile; update submodule URLs to use SSH

Dockerfile

@@ -0,0 +1,26 @@
+FROM node:22.14.0 AS frontend
+
+WORKDIR /frontend
+ADD frontend/ ./
+RUN npm install && npm run build
+
+FROM golang:1.24.4 AS backend
+
+ENV CGO_ENABLED=0
+
+WORKDIR /backend
+ADD backend/ .
+
+RUN go mod download
+RUN go build -o /backend/app
+
+FROM alpine AS runtime
+
+WORKDIR /app
+
+COPY --from=frontend /frontend/dist /app/dist
+COPY --from=backend /backend/app /app/app
+
+EXPOSE 8000
+
+ENTRYPOINT ["/app/app"]