feat: complete remaining Go backend modules

backend/cmd/zhinian-api/main_test.go

@@ -1,6 +1,10 @@
 package main
 
-import "testing"
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
 
 func TestListenAddressDefaultsToLoopbackAndSupportsExplicitBinding(t *testing.T) {
 	if got := listenAddress(func(string) string { return "" }); got != "127.0.0.1:8080" {
@@ -11,3 +15,18 @@ func TestListenAddressDefaultsToLoopbackAndSupportsExplicitBinding(t *testing.T)
 		t.Fatalf("listenAddress(explicit) = %q", got)
 	}
 }
+
+func TestRuntimeGetenvLoadsWhitelistedSettingsAndPreservesProcessPrecedence(t *testing.T) {
+	path := filepath.Join(t.TempDir(), ".env.local")
+	if err := os.WriteFile(path, []byte("IMAGE_GENERATE_ENGINE=evolink\nEVOLINK_API_KEY=file-secret\nDATABASE_URL=postgres://must-not-load\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	process := map[string]string{"ZHINIAN_SETTINGS_FILE": path, "EVOLINK_API_KEY": "process-secret", "ZHINIAN_DATA_BACKEND": "local"}
+	getenv, err := runtimeGetenv(func(name string) string { return process[name] })
+	if err != nil {
+		t.Fatal(err)
+	}
+	if getenv("IMAGE_GENERATE_ENGINE") != "evolink" || getenv("EVOLINK_API_KEY") != "process-secret" || getenv("DATABASE_URL") != "" || getenv("ZHINIAN_DATA_BACKEND") != "local" {
+		t.Fatalf("loaded engine=%q key=%q database=%q backend=%q", getenv("IMAGE_GENERATE_ENGINE"), getenv("EVOLINK_API_KEY"), getenv("DATABASE_URL"), getenv("ZHINIAN_DATA_BACKEND"))
+	}
+}