refactor: introduce Wire dependency injection and interface-based architecture

- Add Google Wire for compile-time dependency injection
- Replace concrete service types with interfaces across handlers
- Remove global state (DB, cache) in favor of constructor injection
- Split monolithic files into focused modules:
  - config: separate files for each config domain
  - dto: converters split by domain (user, post, message, group)
  - cache: separate metrics.go and redis_cache.go
- Introduce unified apperrors package with string-based error codes
- Add transaction support with context-aware repository methods
- Upgrade golang.org/x/crypto from 0.17.0 to 0.26.0

internal/config/cache.go

@@ -0,0 +1,70 @@
+package config
+
+import "time"
+
+// ConversationCacheConfig 会话缓存配置
+type ConversationCacheConfig struct {
+	// TTL 配置
+	DetailTTL      string `mapstructure:"detail_ttl"`
+	ListTTL        string `mapstructure:"list_ttl"`
+	ParticipantTTL string `mapstructure:"participant_ttl"`
+	UnreadTTL      string `mapstructure:"unread_ttl"`
+
+	// 消息缓存配置
+	MessageDetailTTL string `mapstructure:"message_detail_ttl"`
+	MessageListTTL   string `mapstructure:"message_list_ttl"`
+	MessageIndexTTL  string `mapstructure:"message_index_ttl"`
+	MessageCountTTL  string `mapstructure:"message_count_ttl"`
+
+	// 批量写入配置
+	BatchInterval  string `mapstructure:"batch_interval"`
+	BatchThreshold int    `mapstructure:"batch_threshold"`
+	BatchMaxSize   int    `mapstructure:"batch_max_size"`
+	BufferMaxSize  int    `mapstructure:"buffer_max_size"`
+}
+
+// ConversationCacheSettings 会话缓存运行时配置（用于传递给 cache 包）
+type ConversationCacheSettings struct {
+	DetailTTL        time.Duration
+	ListTTL          time.Duration
+	ParticipantTTL   time.Duration
+	UnreadTTL        time.Duration
+	MessageDetailTTL time.Duration
+	MessageListTTL   time.Duration
+	MessageIndexTTL  time.Duration
+	MessageCountTTL  time.Duration
+	BatchInterval    time.Duration
+	BatchThreshold   int
+	BatchMaxSize     int
+	BufferMaxSize    int
+}
+
+// ToSettings 将 ConversationCacheConfig 转换为 ConversationCacheSettings
+func (c *ConversationCacheConfig) ToSettings() *ConversationCacheSettings {
+	return &ConversationCacheSettings{
+		DetailTTL:        parseDuration(c.DetailTTL, 5*time.Minute),
+		ListTTL:          parseDuration(c.ListTTL, 60*time.Second),
+		ParticipantTTL:   parseDuration(c.ParticipantTTL, 5*time.Minute),
+		UnreadTTL:        parseDuration(c.UnreadTTL, 30*time.Second),
+		MessageDetailTTL: parseDuration(c.MessageDetailTTL, 30*time.Minute),
+		MessageListTTL:   parseDuration(c.MessageListTTL, 5*time.Minute),
+		MessageIndexTTL:  parseDuration(c.MessageIndexTTL, 30*time.Minute),
+		MessageCountTTL:  parseDuration(c.MessageCountTTL, 30*time.Minute),
+		BatchInterval:    parseDuration(c.BatchInterval, 5*time.Second),
+		BatchThreshold:   c.BatchThreshold,
+		BatchMaxSize:     c.BatchMaxSize,
+		BufferMaxSize:    c.BufferMaxSize,
+	}
+}
+
+// parseDuration 解析持续时间字符串，如果解析失败则返回默认值
+func parseDuration(s string, defaultVal time.Duration) time.Duration {
+	if s == "" {
+		return defaultVal
+	}
+	d, err := time.ParseDuration(s)
+	if err != nil {
+		return defaultVal
+	}
+	return d
+}