Reapply "feat(loyalty): EnakPoint & EnakCoin" (#32)

This reverts commit 4e24f9bbb0.

internal/service/earning_backfill_job_test.go

@@ -0,0 +1,46 @@
+package service
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+
+	"apskel-pos-be/internal/logger"
+)
+
+type missingEarnerFake struct {
+	since  time.Time
+	max    int
+	earned int
+	err    error
+	calls  int
+}
+
+func (f *missingEarnerFake) EarnMissing(_ context.Context, since time.Time, maxOrders int) (int, int, error) {
+	f.calls++
+	f.since, f.max = since, maxOrders
+	return f.earned * 2, f.earned, f.err
+}
+
+func TestEarningBackfillJob(t *testing.T) {
+	logger.Setup("fatal", "json")
+	now := time.Date(2026, 9, 30, 12, 0, 0, 0, time.UTC)
+	earner := &missingEarnerFake{earned: 3}
+	job := NewEarningBackfillJob(earner)
+	job.now = func() time.Time { return now }
+
+	assert.Equal(t, 3, job.RunOnce(context.Background()))
+	assert.Equal(t, now.Add(-72*time.Hour), earner.since, "looks back three days")
+	assert.Equal(t, earningBackfillMaxOrders, earner.max)
+
+	// A failing run is logged, not fatal.
+	earner.earned, earner.err = 0, errors.New("db down")
+	assert.Equal(t, 0, job.RunOnce(context.Background()))
+
+	job.Start(time.Hour)
+	job.Stop()
+	job.Stop()
+}