feat(loyalty): organization loyalty settings API

Adds GET and PUT /marketing/loyalty-settings and GET
/marketing/loyalty-settings/history (docs/prd-point-coin.md F2, PC-302).

The settings are the point value, the exchange rate, transfer limits and
the stored expiry settings. PUT merges the body like the outlet settings
and is limited to loyalty managers. Every response carries the impact of
the change on the balances in circulation: outstanding EnakPoint and
EnakCoin, their rupiah value, and the coins exchanged into points, before
and after. With ?dry_run=true nothing is saved and the response lists the
keys that would change, for the warning shown before saving.

Saving records each change in loyalty_setting_changes with who made it;
history can be filtered to one outlet. Changing the value leaves what was
already written alone. The diff behind saving and previewing is shared.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/models/loyalty.go

@@ -103,3 +103,57 @@ func LoyaltyCashbackPercent(earnValue, pointValue, earnPerAmount int64) float64
 	}
 	return math.Round(float64(earnValue)*float64(pointValue)*10000/float64(earnPerAmount)) / 100
 }
+
+// OrganizationLoyaltySettingsView is GET and PUT /marketing/loyalty-settings.
+type OrganizationLoyaltySettingsView struct {
+	OrganizationLoyaltySettings
+	// What the balances in circulation are worth, before and after the change.
+	Impact LoyaltySettingsImpact `json:"impact"`
+	// On PUT, the keys that changed; on a dry run, the keys that would.
+	Changes []LoyaltySettingChange `json:"changes"`
+	// True when nothing was saved.
+	DryRun bool `json:"dry_run"`
+}
+
+// LoyaltySettingsImpact shows how a change of point value or exchange rate changes what
+// the balances in circulation are worth (F2). Before and after are equal when neither
+// changes.
+type LoyaltySettingsImpact struct {
+	OutstandingPoints int64 `json:"outstanding_points"`
+	OutstandingCoins  int64 `json:"outstanding_coins"`
+
+	PointValueBefore  int64 `json:"point_value_before"`
+	PointValueAfter   int64 `json:"point_value_after"`
+	PointRupiahBefore int64 `json:"point_rupiah_before"`
+	PointRupiahAfter  int64 `json:"point_rupiah_after"`
+
+	// The coins in circulation exchanged at the rate, in EnakPoint and in rupiah.
+	CoinsAsPointsBefore int64 `json:"coins_as_points_before"`
+	CoinsAsPointsAfter  int64 `json:"coins_as_points_after"`
+	CoinRupiahBefore    int64 `json:"coin_rupiah_before"`
+	CoinRupiahAfter     int64 `json:"coin_rupiah_after"`
+}
+
+// NewLoyaltySettingsImpact computes the impact of moving from one organization setting
+// to another on the balances in circulation.
+func NewLoyaltySettingsImpact(points, coins int64, before, after OrganizationLoyaltySettings) LoyaltySettingsImpact {
+	asPoints := func(s OrganizationLoyaltySettings) int64 {
+		if s.Exchange.CoinAmount <= 0 {
+			return 0
+		}
+		return coins * s.Exchange.PointAmount / s.Exchange.CoinAmount
+	}
+	impact := LoyaltySettingsImpact{
+		OutstandingPoints:   points,
+		OutstandingCoins:    coins,
+		PointValueBefore:    before.PointValue,
+		PointValueAfter:     after.PointValue,
+		PointRupiahBefore:   points * before.PointValue,
+		PointRupiahAfter:    points * after.PointValue,
+		CoinsAsPointsBefore: asPoints(before),
+		CoinsAsPointsAfter:  asPoints(after),
+	}
+	impact.CoinRupiahBefore = impact.CoinsAsPointsBefore * before.PointValue
+	impact.CoinRupiahAfter = impact.CoinsAsPointsAfter * after.PointValue
+	return impact
+}

internal/models/loyalty_test.go

@@ -0,0 +1,32 @@
+package models
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLoyaltyCashbackPercent(t *testing.T) {
+	assert.Equal(t, 1.0, LoyaltyCashbackPercent(1, 1, 100))
+	assert.Equal(t, 0.1, LoyaltyCashbackPercent(1, 1, 1000))
+	assert.Equal(t, 0.33, LoyaltyCashbackPercent(1, 1, 300), "rounded to two decimals")
+	assert.Equal(t, 0.67, LoyaltyCashbackPercent(2, 1, 300), "rounded, not cut")
+	assert.Equal(t, 0.0, LoyaltyCashbackPercent(1, 1, 0))
+}
+
+func TestNewLoyaltySettingsImpact(t *testing.T) {
+	before := OrganizationLoyaltySettings{PointValue: 1, Exchange: LoyaltyExchangeSettings{CoinAmount: 1, PointAmount: 1}}
+	after := OrganizationLoyaltySettings{PointValue: 100, Exchange: LoyaltyExchangeSettings{CoinAmount: 10, PointAmount: 1}}
+
+	got := NewLoyaltySettingsImpact(50000, 105, before, after)
+	assert.Equal(t, LoyaltySettingsImpact{
+		OutstandingPoints: 50000, OutstandingCoins: 105,
+		PointValueBefore: 1, PointValueAfter: 100,
+		PointRupiahBefore: 50000, PointRupiahAfter: 5000000,
+		CoinsAsPointsBefore: 105, CoinsAsPointsAfter: 10, // floor(105 / 10)
+		CoinRupiahBefore: 105, CoinRupiahAfter: 1000,
+	}, got)
+
+	same := NewLoyaltySettingsImpact(10, 10, before, before)
+	assert.Equal(t, same.PointRupiahBefore, same.PointRupiahAfter)
+}