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/service/email_code_service.go

@@ -43,9 +43,6 @@ type emailCodeServiceImpl struct {
 }
 
 func NewEmailCodeService(emailService EmailService, cacheBackend cache.Cache) EmailCodeService {
-	if cacheBackend == nil {
-		cacheBackend = cache.GetCache()
-	}
 	return &emailCodeServiceImpl{
 		emailService: emailService,
 		cache:        cacheBackend,