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/redis.go

@@ -0,0 +1,71 @@
+package config
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/redis/go-redis/v9"
+)
+
+// RedisConfig Redis 配置
+type RedisConfig struct {
+	Type      string            `mapstructure:"type"`
+	Redis     RedisServerConfig `mapstructure:"redis"`
+	Miniredis MiniredisConfig   `mapstructure:"miniredis"`
+	PoolSize  int               `mapstructure:"pool_size"`
+}
+
+// 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"`
+}
+
+// CacheModuleTTL 缓存模块 TTL 配置
+type CacheModuleTTL struct {
+	PostList     int `mapstructure:"post_list_ttl"`
+	Conversation int `mapstructure:"conversation_ttl"`
+	UnreadCount  int `mapstructure:"unread_count_ttl"`
+	GroupMembers int `mapstructure:"group_members_ttl"`
+}
+
+// RedisServerConfig Redis 服务器配置
+type RedisServerConfig struct {
+	Host     string `mapstructure:"host"`
+	Port     int    `mapstructure:"port"`
+	Password string `mapstructure:"password"`
+	DB       int    `mapstructure:"db"`
+}
+
+// Addr 返回 Redis 服务器地址
+func (r RedisServerConfig) Addr() string {
+	return fmt.Sprintf("%s:%d", r.Host, r.Port)
+}
+
+// MiniredisConfig Miniredis 配置（用于测试）
+type MiniredisConfig struct {
+	Host string `mapstructure:"host"`
+	Port int    `mapstructure:"port"`
+}
+
+// NewRedis 创建 Redis 客户端（真实 Redis）
+func NewRedis(cfg *RedisConfig) (*redis.Client, error) {
+	client := redis.NewClient(&redis.Options{
+		Addr:     cfg.Redis.Addr(),
+		Password: cfg.Redis.Password,
+		DB:       cfg.Redis.DB,
+		PoolSize: cfg.PoolSize,
+	})
+
+	ctx := context.Background()
+	if err := client.Ping(ctx).Err(); err != nil {
+		return nil, fmt.Errorf("failed to connect to redis: %w", err)
+	}
+
+	return client, nil
+}