refactor: unify database url configuration

Consolidate source/target connection handling around a single URL-based configuration model.

internal/app/config/main.go

@@ -7,13 +7,9 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-type dbConfig struct {
-	Url string
-}
-
 type appConfig struct {
-	FromDb dbConfig
-	ToDb   dbConfig
+	SourceDbUrl string
+	TargetDbUrl string
 }
 
 func loadEnv() {
@@ -26,23 +22,19 @@ func loadEnv() {
 func getAppConfig() appConfig {
 	loadEnv()
 
-	fromDbUrl := os.Getenv("PG_FROM_DB_URL")
-	if fromDbUrl == "" {
-		log.Fatal("PG_FROM_DB_URL environment variable not set")
+	sourceDbUrl := os.Getenv("SOURCE_DB_URL")
+	if sourceDbUrl == "" {
+		log.Fatal("SOURCE_DB_URL environment variable not set")
 	}
 
-	toDbUrl := os.Getenv("PG_TO_DB_URL")
-	if toDbUrl == "" {
-		log.Fatal("PG_TO_DB_URL environment variable not set")
+	targetDbUrl := os.Getenv("TARGET_DB_URL")
+	if targetDbUrl == "" {
+		log.Fatal("TARGET_DB_URL environment variable not set")
 	}
 
 	return appConfig{
-		FromDb: dbConfig{
-			Url: fromDbUrl,
-		},
-		ToDb: dbConfig{
-			Url: toDbUrl,
-		},
+		SourceDbUrl: sourceDbUrl,
+		TargetDbUrl: targetDbUrl,
 	}
 }