feat(loyalty): typed loyalty settings with change history

Adds LoyaltySettingsProcessor (docs/prd-point-coin.md F1, F2, F12, PC-109).

Reading returns typed settings for an outlet (earning per currency, paying
with EnakPoint) and for an organization (point value, exchange rate,
transfers, and the expiry settings awaiting note N4). A key that was never
set takes the PRD default. A stored value that is unusable, such as an
earn_per_amount of 0 that would divide by zero, also falls back to the
default and is logged, so a bad row never reaches a calculation.

Writing takes the whole settings struct, validates every rule in the PRD
before touching the database, and stores and records in
loyalty_setting_changes only the keys whose effective value changes: old
value (NULL while it was on its default), new value, and who changed it.
Clearing a limit deletes the stored value. Each save runs in one
transaction under an advisory lock per outlet or organization, so two saves
at once cannot both compute their change from the same old value. The
outlet must belong to the caller's organization.

Every key is described once (key, default, valid range, bound field), and
reading, validating and diffing all use that description.

GET /customer/wallet now reads the point value through this processor; the
minimal organization settings repository from PC-106 is removed.

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

internal/models/loyalty.go

@@ -0,0 +1,81 @@
+package models
+
+import (
+	"time"
+
+	"github.com/google/uuid"
+)
+
+// OutletLoyaltySettings are an outlet's loyalty settings (docs/prd-point-coin.md F1).
+type OutletLoyaltySettings struct {
+	Point LoyaltyEarnSettings `json:"point"`
+	Coin  LoyaltyEarnSettings `json:"coin"`
+	// Paying with EnakPoint. EnakCoin cannot pay, so it has no counterpart.
+	PointPayment LoyaltyPointPaymentSettings `json:"point_payment"`
+}
+
+// LoyaltyEarnSettings is how much of one currency an order earns:
+// floor(basis / EarnPerAmount) × EarnValue, nothing below MinOrderAmount, and at most
+// MaxPerOrder when set.
+type LoyaltyEarnSettings struct {
+	Enabled        bool   `json:"enabled"`
+	EarnPerAmount  int64  `json:"earn_per_amount"`
+	EarnValue      int64  `json:"earn_value"`
+	MinOrderAmount int64  `json:"min_order_amount"`
+	MaxPerOrder    *int64 `json:"max_per_order"`
+}
+
+type LoyaltyPointPaymentSettings struct {
+	AcceptPayment    bool  `json:"accept_payment"`
+	MinPaymentPoints int64 `json:"min_payment_points"`
+	// Largest share of the order total, 0–100, that EnakPoint may pay.
+	MaxPaymentPercent int64 `json:"max_payment_percent"`
+}
+
+// OrganizationLoyaltySettings are the loyalty settings shared by every outlet of an
+// organization (docs/prd-point-coin.md F2, F12).
+type OrganizationLoyaltySettings struct {
+	// Rupiah value of one EnakPoint when paying.
+	PointValue int64 `json:"point_value"`
+	// CoinAmount EnakCoin exchange into PointAmount EnakPoint.
+	Exchange    LoyaltyExchangeSettings `json:"exchange"`
+	Transfer    LoyaltyTransferSettings `json:"transfer"`
+	PointExpiry LoyaltyExpirySettings   `json:"point_expiry"`
+	CoinExpiry  LoyaltyExpirySettings   `json:"coin_expiry"`
+}
+
+type LoyaltyExchangeSettings struct {
+	CoinAmount  int64 `json:"coin_amount"`
+	PointAmount int64 `json:"point_amount"`
+}
+
+type LoyaltyTransferSettings struct {
+	Enabled           bool   `json:"enabled"`
+	MinAmount         int64  `json:"min_amount"`
+	MaxPerTransaction *int64 `json:"max_per_transaction"`
+	DailyLimit        *int64 `json:"daily_limit"`
+}
+
+// LoyaltyExpirySettings is how long one currency lasts once received. The expiry
+// model is still open (note N4); these are only the stored settings.
+type LoyaltyExpirySettings struct {
+	Enabled bool  `json:"enabled"`
+	Period  int64 `json:"period"`
+	// DAY or MONTH.
+	Unit         string `json:"unit"`
+	EndOfMonth   bool   `json:"end_of_month"`
+	ReminderDays int64  `json:"reminder_days"`
+}
+
+// LoyaltySettingChange is one row of the loyalty settings history.
+type LoyaltySettingChange struct {
+	ID             uuid.UUID  `json:"id"`
+	OrganizationID uuid.UUID  `json:"organization_id"`
+	OutletID       *uuid.UUID `json:"outlet_id"`
+	Key            string     `json:"key"`
+	// Nil when the key had no stored value, that is it was on its default.
+	OldValue  *string   `json:"old_value"`
+	NewValue  *string   `json:"new_value"`
+	ChangedBy uuid.UUID `json:"changed_by"`
+	CreatedAt time.Time `json:"created_at"`
+}