fix(heicode-self): quota_display_type 补 CUSTOM + 统一大写 + 加 displayQuota 测试

按 Mem0ried 复审：
- quotaDisplayUnitLabel 补 QuotaDisplayTypeCustom 分支（原落 default→"USD"，
  导致自定义币种站点 display_quota 算对但 type 误报 USD、客户端配错符号）。
- tokens 标签由小写 "tokens" 改为规范常量 TOKENS，displayQuota 的判断同步用常量，
  对外 quota_display_type 统一大写（与 USD/CNY/CUSTOM 一致，客户端按常量比较不再 mismatch）。
- 新增表驱动测试 heicode_self_test.go：displayQuota 四模式（USD 除 / CNY·CUSTOM 乘 /
  TOKENS 原值）+ per_unit<=0 防除零；quotaDisplayUnitLabel 四模式（含 CUSTOM 回归）。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

heicode/controller/heicode_self.go

@@ -11,16 +11,23 @@ import (
 	"github.com/heicode/manager/setting/operation_setting"
 )
 
-// quotaDisplayUnitLabel names the unit the raw quota is denominated in.
+// quotaDisplayUnitLabel names the unit the raw quota is denominated in. Returns
-// Returns USD / CNY / tokens (mirrors the web dashboard's quota display type).
+// the canonical (UPPER-CASE) display-type constant — USD / CNY / TOKENS / CUSTOM
+// — mirroring the web dashboard. The client uses this only to pick a currency
+// symbol; the actual conversion is done server-side (display_quota). Returning the
+// constants verbatim keeps the wire value byte-identical to what the client
+// compares against, and covers CUSTOM (previously fell through to "USD", so a
+// custom-currency site mislabelled its display_quota and the client showed "$").
 func quotaDisplayUnitLabel() string {
 	switch operation_setting.GetQuotaDisplayType() {
 	case operation_setting.QuotaDisplayTypeCNY:
-		return "CNY"
+		return operation_setting.QuotaDisplayTypeCNY
 	case operation_setting.QuotaDisplayTypeTokens:
-		return "tokens"
+		return operation_setting.QuotaDisplayTypeTokens
+	case operation_setting.QuotaDisplayTypeCustom:
+		return operation_setting.QuotaDisplayTypeCustom
 	default:
-		return "USD"
+		return operation_setting.QuotaDisplayTypeUSD
 	}
 }
 
@@ -31,12 +38,12 @@ func quotaDisplayUnitLabel() string {
 //	USD    : raw / quota_per_unit
 //	CNY    : raw / quota_per_unit * usd_exchange_rate
 //	CUSTOM : raw / quota_per_unit * custom_currency_exchange_rate
-//	tokens : raw                                   (no division)
+//	TOKENS : raw                                   (no division)
 //
 // usd_exchange_rate is the USD→display-currency multiplier returned alongside,
 // so clients that prefer raw can recompute the same value.
 func displayQuota(raw int, label string, perUnit, rate float64) float64 {
-	if label == "tokens" || perUnit <= 0 {
+	if label == operation_setting.QuotaDisplayTypeTokens || perUnit <= 0 {
 		return float64(raw)
 	}
 	return float64(raw) / perUnit * rate
@@ -93,7 +100,7 @@ func GetHeicodeSelf(c *gin.Context) {
 			"quota":              user.Quota,
 			"used_quota":         user.UsedQuota,
 			"quota_per_unit":     common.QuotaPerUnit,
-			"quota_display_type": label, // USD / CNY / tokens
+			"quota_display_type": label, // USD / CNY / TOKENS / CUSTOM (pick currency symbol only)
 			"usd_exchange_rate":  rate,  // USD→display-currency multiplier (1 for USD/tokens)
 			// ready-to-show values (server applies the display-type formula above).
 			"display_quota":      displayQuota(user.Quota, label, perUnit, rate),

heicode/controller/heicode_self_test.go

@@ -0,0 +1,55 @@
+package controller
+
+import (
+	"testing"
+
+	"github.com/heicode/manager/setting/operation_setting"
+	"github.com/stretchr/testify/require"
+)
+
+// displayQuota is the /api/heicode/self conversion contract: the server applies
+// the display-type formula so the client never special-cases a mode. Pin all
+// four modes (USD divides, CNY/CUSTOM scale, TOKENS passes through) and the
+// divide-by-zero guard.
+func TestDisplayQuota_AllModes(t *testing.T) {
+	const perUnit = 500000.0
+	cases := []struct {
+		name  string
+		raw   int
+		label string
+		rate  float64
+		want  float64
+	}{
+		{"USD divides by per-unit", 1_000_000, operation_setting.QuotaDisplayTypeUSD, 1, 2},
+		{"CNY multiplies by usd rate", 1_000_000, operation_setting.QuotaDisplayTypeCNY, 7.3, 14.6},
+		{"CUSTOM uses custom rate", 1_000_000, operation_setting.QuotaDisplayTypeCustom, 2.5, 5},
+		{"TOKENS returns raw, no division", 1_000_000, operation_setting.QuotaDisplayTypeTokens, 1, 1_000_000},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			require.InDelta(t, tc.want, displayQuota(tc.raw, tc.label, perUnit, tc.rate), 1e-9)
+		})
+	}
+
+	// per_unit<=0 must never divide by zero — return raw unchanged.
+	require.Equal(t, float64(1_000_000), displayQuota(1_000_000, operation_setting.QuotaDisplayTypeUSD, 0, 1))
+}
+
+// quotaDisplayUnitLabel must echo the canonical UPPER-CASE constant for every
+// mode. The CUSTOM case is the regression guard: it previously fell through to
+// "USD", mislabelling a custom-currency site's display_quota.
+func TestQuotaDisplayUnitLabel_CanonicalAndCustom(t *testing.T) {
+	gs := operation_setting.GetGeneralSetting()
+	orig := gs.QuotaDisplayType
+	t.Cleanup(func() { gs.QuotaDisplayType = orig })
+
+	for _, want := range []string{
+		operation_setting.QuotaDisplayTypeUSD,
+		operation_setting.QuotaDisplayTypeCNY,
+		operation_setting.QuotaDisplayTypeTokens,
+		operation_setting.QuotaDisplayTypeCustom,
+	} {
+		gs.QuotaDisplayType = want
+		require.Equal(t, want, quotaDisplayUnitLabel())
+	}
+}