feat: Redis/MongoDB分页+CSV导出全数据库类型支持

后端:
- Redis 分页: KEYS→SCAN分页, LRANGE→offset/limit, SMEMBERS→SSCAN分页
- MongoDB 新增 executeMongoQuery: db.collection.find/aggregate 解析
  - find: skip/limit分页 + CountDocuments总数
  - aggregate: $facet并行取count+data
  - bson.M扁平化处理嵌套文档
- ExportQueryCSV 改为多分支: exportSQLCSV/exportRedisCSV/exportMongoCSV
  - Redis: 复用executeRedisQuery取数据写CSV
  - MongoDB: 复用executeMongoQuery取数据写CSV
- 新增 mongo-driver v2 依赖
- 前端: Redis也显示导出CSV按钮(去掉dbType过滤)

backend/go.mod

@@ -38,6 +38,7 @@ require (
 	github.com/jinzhu/inflection v1.0.0 // indirect
 	github.com/jinzhu/now v1.1.5 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/klauspost/compress v1.17.6 // indirect
 	github.com/klauspost/cpuid/v2 v2.2.10 // indirect
 	github.com/kr/text v0.2.0 // indirect
 	github.com/leodido/go-urn v1.4.0 // indirect
@@ -48,6 +49,11 @@ require (
 	github.com/pelletier/go-toml/v2 v2.2.3 // indirect
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
 	github.com/ugorji/go/codec v1.2.12 // indirect
+	github.com/xdg-go/pbkdf2 v1.0.0 // indirect
+	github.com/xdg-go/scram v1.2.0 // indirect
+	github.com/xdg-go/stringprep v1.0.4 // indirect
+	github.com/youmark/pkcs8 v0.0.0-20240726163527-a2c0da244d78 // indirect
+	go.mongodb.org/mongo-driver/v2 v2.6.0 // indirect
 	go.uber.org/atomic v1.11.0 // indirect
 	golang.org/x/arch v0.15.0 // indirect
 	golang.org/x/net v0.50.0 // indirect