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/model/json_helper.go

@@ -0,0 +1,28 @@
+package model
+
+import (
+	"database/sql/driver"
+	"encoding/json"
+)
+
+// ScanJSON scans a database value (nil, []byte, or string) into any JSON-unmarshalable pointer.
+func ScanJSON[T any](ptr *T, value any) error {
+	if value == nil {
+		return nil
+	}
+	var data []byte
+	switch v := value.(type) {
+	case []byte:
+		data = v
+	case string:
+		data = []byte(v)
+	default:
+		return nil
+	}
+	return json.Unmarshal(data, ptr)
+}
+
+// ValueJSON marshals any value to JSON for database storage.
+func ValueJSON[T any](val T) (driver.Value, error) {
+	return json.Marshal(val)
+}