feat: Add project foundation, documentation, and Docker setup

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/Dockerfile.dev

@@ -0,0 +1,18 @@
+FROM golang:1.25.6-bookworm
+
+WORKDIR /app
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    git \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+
+RUN go build -o server ./cmd/server
+
+EXPOSE 8080
+
+CMD ["./server"]