feat: add hook system, QR code login, and layered cache

- Implement extensible hook system for content moderation with
  builtin and AI-powered moderation hooks
- Add QR code login feature with SSE for real-time status updates
  and scan/confirm/cancel workflow
- Introduce layered cache with local LRU + Redis backend for
  improved read performance
- Refactor post and comment services to use hook-based moderation
  instead of direct AI service calls
- Add local cache configuration options (size, buckets, ttl)

internal/config/config.go

@@ -72,6 +72,10 @@ func Load(configPath string) (*Config, error) {
 	viper.SetDefault("cache.modules.conversation_ttl", 60)
 	viper.SetDefault("cache.modules.unread_count_ttl", 30)
 	viper.SetDefault("cache.modules.group_members_ttl", 120)
+	viper.SetDefault("cache.local.enabled", true)
+	viper.SetDefault("cache.local.size", 10000)
+	viper.SetDefault("cache.local.buckets", 0)
+	viper.SetDefault("cache.local.default_ttl", 300)
 	viper.SetDefault("jwt.secret", "your-jwt-secret-key-change-in-production")
 	viper.SetDefault("jwt.access_token_expire", 86400)
 	viper.SetDefault("jwt.refresh_token_expire", 604800)

internal/config/redis.go

@@ -17,13 +17,22 @@ type RedisConfig struct {
 
 // CacheConfig 缓存配置
 type CacheConfig struct {
-	Enabled        bool           `mapstructure:"enabled"`
-	KeyPrefix      string         `mapstructure:"key_prefix"`
-	DefaultTTL     int            `mapstructure:"default_ttl"`
-	NullTTL        int            `mapstructure:"null_ttl"`
-	JitterRatio    float64        `mapstructure:"jitter_ratio"`
-	DisableFlushDB bool           `mapstructure:"disable_flushdb"`
-	Modules        CacheModuleTTL `mapstructure:"modules"`
+	Enabled        bool             `mapstructure:"enabled"`
+	KeyPrefix      string           `mapstructure:"key_prefix"`
+	DefaultTTL     int              `mapstructure:"default_ttl"`
+	NullTTL        int              `mapstructure:"null_ttl"`
+	JitterRatio    float64          `mapstructure:"jitter_ratio"`
+	DisableFlushDB bool             `mapstructure:"disable_flushdb"`
+	Modules        CacheModuleTTL   `mapstructure:"modules"`
+	Local          LocalCacheConfig `mapstructure:"local"`
+}
+
+// LocalCacheConfig 本地缓存配置
+type LocalCacheConfig struct {
+	Enabled    bool `mapstructure:"enabled"`
+	Size       int  `mapstructure:"size"`
+	Buckets    int  `mapstructure:"buckets"`
+	DefaultTTL int  `mapstructure:"default_ttl"`
 }
 
 // CacheModuleTTL 缓存模块 TTL 配置