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/wire/provider_set.go

@@ -0,0 +1,11 @@
+package wire
+
+import "github.com/google/wire"
+
+// AllSet 包含所有 Provider Set
+var AllSet = wire.NewSet(
+	InfrastructureSet,
+	RepositorySet,
+	ServiceSet,
+	HandlerSet,
+)