refac: runtime settings are read once at startup and passed in through the composition root; no handler, router or repository reads environment variables

test/image_extension_mapping_test.go

@@ -15,8 +15,7 @@ func TestImageRepositoryHasAnExtensionForEveryAllowedContentType(t *testing.T) {
 	if err := db.AutoMigrate(&models.Image{}); err != nil {
 		t.Fatalf("failed to migrate: %v", err)
 	}
-	repo := persistence.NewImageRepository(db)
-	t.Setenv("UPLOAD_DIR", t.TempDir())
+	repo := persistence.NewImageRepository(db, t.TempDir())
 
 	allowedContentTypes := imageDomain.AllowedContentTypes()
 	expectedContentTypes := []string{"image/jpeg", "image/png", "image/svg+xml", "image/webp"}