feat: 添加货币格式化配置，支持自定义小数位和分隔符，增强 API 响应的可读性

app/Support/CurrencyFormatter.php

@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Support;
+
+/**
+ * 将「最小货币单位」整数格式化为展示用字符串（不改变业务数字，仅格式化）。
+ *
+ * 拆分位数由 {@see config('lottery.ui.format.currency.decimals')} 决定，默认 2（即 ÷100）。
+ */
+final class CurrencyFormatter
+{
+    public static function fromMinor(int|string|null $minor): string
+    {
+        if ($minor === null || $minor === '') {
+            return self::formatMinorInt(0);
+        }
+
+        return self::formatMinorInt((int) $minor);
+    }
+
+    private static function formatMinorInt(int $minorUnits): string
+    {
+        $decimals = max(0, min(12, (int) config('lottery.ui.format.currency.decimals', 2)));
+        $decSep = (string) config('lottery.ui.format.currency.decimal_separator', '.');
+        $thousandsSep = (string) config('lottery.ui.format.currency.thousands_separator', ',');
+
+        $divisor = (int) max(1, 10 ** $decimals);
+        $negative = $minorUnits < 0;
+        $abs = abs($minorUnits);
+
+        $integerPart = intdiv($abs, $divisor);
+        $fractionRaw = $abs % $divisor;
+        $fractionPadded = str_pad((string) $fractionRaw, $decimals, '0', STR_PAD_LEFT);
+
+        $integerPartFormatted = number_format((float) $integerPart, 0, $decSep, $thousandsSep);
+
+        if ($decimals === 0) {
+            return ($negative ? '-' : '').$integerPartFormatted;
+        }
+
+        return ($negative ? '-' : '').$integerPartFormatted.$decSep.$fractionPadded;
+    }
+}