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/cache/layered_cache.go

@@ -111,7 +111,11 @@ func (c *LayeredCache) Get(key string) (any, bool) {
 			c.mu.Unlock()
 
 			if ttl := c.getLocalTTL(); ttl > 0 {
-				c.local.Set(key, val, ttl)
+				if str, ok := val.(string); ok {
+					c.local.SetRaw(key, []byte(str), ttl)
+				} else {
+					c.local.Set(key, val, ttl)
+				}
 			}
 			return val, true
 		}
@@ -157,6 +161,23 @@ func (c *LayeredCache) DeleteByPrefix(prefix string) {
 	}
 }
 
+func (c *LayeredCache) DeleteBatch(keys []string) {
+	if !c.enabled || len(keys) == 0 {
+		return
+	}
+
+	c.mu.Lock()
+	c.stats.Invalidates += int64(len(keys))
+	c.mu.Unlock()
+
+	for _, k := range keys {
+		c.local.Delete(k)
+	}
+	if c.redis != nil {
+		c.redis.DeleteBatch(keys)
+	}
+}
+
 func (c *LayeredCache) Clear() {
 	c.local.Clear()
 	if c.redis != nil {