feat: add billing and usage domain cores

backend/internal/postgres/usage_test.go

@@ -0,0 +1,33 @@
+package postgres
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"git.nianxx.cn/wangxuming/NianAIGC/backend/internal/usage"
+)
+
+func TestInsertUsageEventUsesJobConflictForDedupe(t *testing.T) {
+	q := &fakeQuerier{}
+	db := NewDatabase(Config{Backend: BackendPostgres}, q)
+	_, inserted, err := db.InsertUsageEvent(context.Background(), usage.Event{ID: "e", JobID: "j", OwnerID: "a", Source: "platform", Quantity: 1})
+	if err != nil || inserted {
+		t.Fatalf("inserted=%v err=%v", inserted, err)
+	}
+	if q.sql != InsertUsageEventSQL || !strings.Contains(q.sql, "ON CONFLICT (job_id) DO NOTHING") {
+		t.Fatalf("sql=%q", q.sql)
+	}
+}
+
+func TestListUsageEventsUsesExplicitColumnsAndFilters(t *testing.T) {
+	q := &fakeQuerier{}
+	db := NewDatabase(Config{Backend: BackendPostgres}, q)
+	_, err := db.ListUsageEvents(context.Background(), usage.Filters{OwnerID: "a", OrganizationID: "o", From: "2026-01-01", To: "2026-02-01"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if q.sql != ListUsageEventsSQL || len(q.args) != 4 {
+		t.Fatalf("sql=%q args=%#v", q.sql, q.args)
+	}
+}