feat(customer): list the customer's outlets

Adds GET /customer/outlets for the customer app: the active outlets of the
customer's organization, where their EnakPoint and EnakCoin can be used,
sorted by name. Each carries its name and address, and from the outlet's
loyalty settings whether the cashier accepts EnakPoint and whether orders
there earn EnakPoint or EnakCoin. Nothing internal (printer settings, tax
rate) is exposed.

The outlets list under /outlets needs a staff token, so the app had no way
to show where the wallet works.

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

internal/models/customer_outlet.go

@@ -0,0 +1,16 @@
+package models
+
+import "github.com/google/uuid"
+
+// CustomerOutlet is one outlet in GET /customer/outlets: where the customer can shop,
+// and what the outlet does with EnakPoint and EnakCoin.
+type CustomerOutlet struct {
+	ID      uuid.UUID `json:"id"`
+	Name    string    `json:"name"`
+	Address *string   `json:"address"`
+	// The cashier accepts EnakPoint as payment here.
+	AcceptsPointPayment bool `json:"accepts_point_payment"`
+	// Orders here earn EnakPoint / EnakCoin.
+	EarnsPoints bool `json:"earns_points"`
+	EarnsCoins  bool `json:"earns_coins"`
+}