refactor: improve system stability, performance, and code structure

This commit introduces several architectural improvements and optimizations across the codebase:

- **Performance & Reliability**:
  - Implemented Redis pipelining in `ConversationCache.CacheMessage` to reduce network round-trips.
  - Added a circuit breaker to the JPush client to prevent cascading failures.
  - Introduced batch deletion and batch member addition capabilities in repositories.
  - Added message idempotency support using `client_msg_id` and a Redis-based cache.
  - Optimized WebSocket handling with connection limits (total and per-user) and improved error logging.

- **Code Refactoring**:
  - Refactored `Router` to use a `RouterDeps` struct, simplifying the constructor and improving maintainability.
  - Unified model ID generation logic using new `id_helper.go` (supporting UUID and Snowflake).
  - Standardized JSON serialization/deserialization in models using `json_helper.go`.
  - Refactored DTO conversion logic, specifically for `UserResponse` (using functional options) and `Report` responses.
  - Removed redundant/deprecated DTOs like `PostDetailResponse` and `TradeItemDetailResponse`.

- **Cache Improvements**:
  - Enhanced `LayeredCache` with `SetRaw` to avoid double-encoding when promoting values from Redis to local cache.
  - Added `DeleteBatch` support to the cache interface.

- **Other Changes**:
  - Cleaned up `config.go` by removing redundant default values and explicit environment variable overrides.
  - Improved WebSocket registration flow to handle connection limits gracefully.

internal/repository/group_join_request_repo.go

@@ -1,6 +1,8 @@
 package repository
 
 import (
+	"errors"
+
 	"with_you/internal/model"
 
 	"gorm.io/gorm"
@@ -11,6 +13,7 @@ type GroupJoinRequestRepository interface {
 	GetByFlag(flag string) (*model.GroupJoinRequest, error)
 	Update(req *model.GroupJoinRequest) error
 	GetPendingByGroupAndTarget(groupID, targetUserID string, reqType model.GroupJoinRequestType) (*model.GroupJoinRequest, error)
+	GetPendingByGroupAndTargets(groupID string, targetUserIDs []string, reqType model.GroupJoinRequestType) (map[string]bool, error)
 }
 
 type groupJoinRequestRepository struct {
@@ -48,3 +51,25 @@ func (r *groupJoinRequestRepository) GetPendingByGroupAndTarget(groupID, targetU
 	}
 	return &req, nil
 }
+
+func (r *groupJoinRequestRepository) GetPendingByGroupAndTargets(groupID string, targetUserIDs []string, reqType model.GroupJoinRequestType) (map[string]bool, error) {
+	result := make(map[string]bool)
+	if len(targetUserIDs) == 0 {
+		return result, nil
+	}
+	var existingIDs []string
+	err := r.db.Model(&model.GroupJoinRequest{}).
+		Where("group_id = ? AND target_user_id IN ? AND request_type = ? AND status = ?",
+			groupID, targetUserIDs, reqType, model.GroupJoinRequestStatusPending).
+		Pluck("target_user_id", &existingIDs).Error
+	if err != nil {
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			return result, nil
+		}
+		return nil, err
+	}
+	for _, id := range existingIDs {
+		result[id] = true
+	}
+	return result, nil
+}