feat: 数据库定时备份与恢复（S3 兼容存储，支持 Cloudflare R2）

新增管理员专属的数据库备份与恢复功能：
- 全量 PostgreSQL 备份（pg_dump），gzip 压缩后上传到 S3 兼容存储
- 支持手动备份和 cron 定时备份
- 支持从备份恢复（psql --single-transaction）
- 备份文件自动过期清理（默认 14 天）
- 前端完整管理页面（S3 配置、定时配置、备份列表、恢复/下载/删除）
- 内置 Cloudflare R2 配置教程弹窗
- Dockerfile 从 postgres 镜像多阶段复制 pg_dump/psql，确保版本一致

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Dockerfile

@@ -9,6 +9,7 @@
 ARG NODE_IMAGE=node:24-alpine
 ARG GOLANG_IMAGE=golang:1.26.1-alpine
 ARG ALPINE_IMAGE=alpine:3.21
+ARG POSTGRES_IMAGE=postgres:18-alpine
 ARG GOPROXY=https://goproxy.cn,direct
 ARG GOSUMDB=sum.golang.google.cn
 
@@ -73,7 +74,12 @@ RUN VERSION_VALUE="${VERSION}" && \
     ./cmd/server
 
 # -----------------------------------------------------------------------------
-# Stage 3: Final Runtime Image
+# Stage 3: PostgreSQL Client (version-matched with docker-compose)
+# -----------------------------------------------------------------------------
+FROM ${POSTGRES_IMAGE} AS pg-client
+
+# -----------------------------------------------------------------------------
+# Stage 4: Final Runtime Image
 # -----------------------------------------------------------------------------
 FROM ${ALPINE_IMAGE}
 
@@ -86,8 +92,20 @@ LABEL org.opencontainers.image.source="https://github.com/Wei-Shaw/sub2api"
 RUN apk add --no-cache \
     ca-certificates \
     tzdata \
+    libpq \
+    zstd-libs \
+    lz4-libs \
+    krb5-libs \
+    libldap \
+    libedit \
     && rm -rf /var/cache/apk/*
 
+# Copy pg_dump and psql from the same postgres image used in docker-compose
+# This ensures version consistency between backup tools and the database server
+COPY --from=pg-client /usr/local/bin/pg_dump /usr/local/bin/pg_dump
+COPY --from=pg-client /usr/local/bin/psql /usr/local/bin/psql
+COPY --from=pg-client /usr/local/lib/libpq.so.5* /usr/local/lib/
+
 # Create non-root user
 RUN addgroup -g 1000 sub2api && \
     adduser -u 1000 -G sub2api -s /bin/sh -D sub2api