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

go.mod

@@ -7,17 +7,18 @@ require (
 	github.com/gin-gonic/gin v1.9.1
 	github.com/golang-jwt/jwt/v5 v5.2.0
 	github.com/google/uuid v1.5.0
+	github.com/google/wire v0.7.0
 	github.com/gorse-io/gorse-go v0.5.0-alpha.3
 	github.com/minio/minio-go/v7 v7.0.66
 	github.com/redis/go-redis/v9 v9.3.1
 	github.com/spf13/viper v1.18.2
 	go.uber.org/zap v1.26.0
-	golang.org/x/crypto v0.17.0
+	golang.org/x/crypto v0.26.0
 	golang.org/x/image v0.24.0
+	gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df
 	gorm.io/driver/postgres v1.5.4
 	gorm.io/driver/sqlite v1.5.4
 	gorm.io/gorm v1.25.5
-	gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df
 )
 
 require (
@@ -75,8 +76,8 @@ require (
 	go.uber.org/multierr v1.10.0 // indirect
 	golang.org/x/arch v0.3.0 // indirect
 	golang.org/x/exp v0.0.0-20230905200255-921286631fa9 // indirect
-	golang.org/x/net v0.19.0 // indirect
-	golang.org/x/sys v0.15.0 // indirect
+	golang.org/x/net v0.28.0 // indirect
+	golang.org/x/sys v0.23.0 // indirect
 	golang.org/x/text v0.22.0 // indirect
 	google.golang.org/protobuf v1.31.0 // indirect
 	gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc // indirect