重构项目结构：统一目录层级

- 移除 backend/.git 工作树配置
- 将原根目录文件归入 backend/ 目录
- 新增 app/、frontend/ 等模块
- 保留文件历史（自动识别重命名）

backend/services/user-service/user-register-email/Dockerfile

@@ -0,0 +1,33 @@
+FROM rust:1.94.1-alpine3.23 AS builder
+
+RUN apk add --no-cache musl-dev openssl-dev openssl-libs-static pkgconfig
+
+WORKDIR /app
+
+COPY services/user-service/user-register-email/Cargo.toml services/user-service/user-register-email/Cargo.lock* ./
+
+RUN mkdir -p src && echo 'fn main() {}' > src/main.rs
+RUN cargo build --release 2>/dev/null || true
+RUN rm -rf src
+
+COPY services/user-service/user-register-email/src ./src
+
+RUN touch src/main.rs && cargo build --release
+
+FROM alpine:3.23 AS runtime
+
+RUN apk add --no-cache ca-certificates
+
+RUN addgroup -g 1000 appuser && adduser -D -u 1000 -G appuser appuser
+
+WORKDIR /app
+
+COPY --from=builder /app/target/release/user-register-email /app/user-register-email
+
+RUN chown -R appuser:appuser /app
+
+USER appuser
+
+EXPOSE 8080
+
+CMD ["./user-register-email"]