refactor: explicit initialization and dependency injection

- Replace init() with config.Load() function when loading env variables
- Inject portRegistry into session, server, and lifecycle structs
- Inject sessionRegistry directly into interaction and lifecycle
- Remove SetSessionRegistry function and global port variables
- Pass ssh.Conn directly to forwarder constructor instead of lifecycle interface
- Pass user and closeFunc callback to interaction constructor instead of lifecycle interface
- Eliminate circular dependencies between lifecycle, forwarder, and interaction
- Remove setter methods (SetLifecycle) from forwarder and interaction interfaces

internal/config/config.go

@@ -1,19 +1,17 @@
 package config
 
 import (
-	"log"
 	"os"
 	"strconv"
 
 	"github.com/joho/godotenv"
 )
 
-func init() {
+func Load() error {
 	if _, err := os.Stat(".env"); err == nil {
-		if err := godotenv.Load(".env"); err != nil {
-			log.Printf("Warning: Failed to load .env file: %s", err)
-		}
+		return godotenv.Load(".env")
 	}
+	return nil
 }
 
 func Getenv(key, defaultValue string) string {