fix(logger): remove init() function that was overriding config level

Problem: Logger was always using info level despite MPC_LOGGER_LEVEL=debug
Root cause: The init() function in logger.go was calling InitProduction()
which created a zap.NewProduction() logger with hardcoded info level.
This happened before main() called logger.Init(cfg), so the config was
being ignored.

Solution:
1. Removed init() function to prevent early logger initialization
2. Added zap.ReplaceGlobals() in Init() to ensure config takes effect
3. Removed unused "os" import

References:
- https://pkg.go.dev/go.uber.org/zap
- https://stackoverflow.com/questions/57745017/

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/mpc-system/pkg/logger/logger.go

@@ -1,8 +1,6 @@
 package logger
 
 import (
-	"os"
-
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
 )
@@ -70,6 +68,10 @@ func Init(cfg *Config) error {
 	}
 
 	Sugar = Log.Sugar()
+
+	// Replace global zap logger to ensure our config takes effect
+	zap.ReplaceGlobals(Log)
+
 	return nil
 }
 
@@ -158,12 +160,14 @@ func Err(err error) zap.Field {
 	return zap.Error(err)
 }
 
-func init() {
-	// Initialize with development logger by default
-	// This will be overridden when Init() is called with proper config
-	if os.Getenv("ENV") == "production" {
-		_ = InitProduction()
-	} else {
-		_ = InitDevelopment()
-	}
-}
+// Removed init() function to prevent it from overriding logger config.
+// The logger will be initialized when Init() is explicitly called with config.
+// func init() {
+// 	// Initialize with development logger by default
+// 	// This will be overridden when Init() is called with proper config
+// 	if os.Getenv("ENV") == "production" {
+// 		_ = InitProduction()
+// 	} else {
+// 		_ = InitDevelopment()
+// 	}
+// }