feat(mining-app): 市场数据3个小数字段显示后端返回的完整精度

原先 formatCompact/formatWithCommas 内部用 double 运算，double 有效精度
仅约15-16位，对大数值(如98亿)除以1e8后小数部分会丢失精度。
后端 3 个字段均为 Decimal(30,8)，通过 toFixed(8) 返回 8 位小数。

新增 formatCompactFull / formatWithCommasFull 函数:
- _shiftDecimalLeft: 纯字符串小数点移位，不经 double 转换，零精度损失
- _addCommasFullPrecision: 整数部分加千位逗号 + 小数部分原样保留
- formatCompactFull: 万/亿缩写 + 完整后端精度（替代 formatCompact）
- formatWithCommasFull: 逗号分隔 + 完整后端精度（替代 formatWithCommas）

兑换页 (trading_page.dart) 修改:
- 剩余积分股: formatCompact(precision:4) → formatCompactFull (8位小数)
- 已分配积分股: formatCompact(precision:2) → formatCompactFull (8位小数)
- 积分股池: formatWithCommas → formatWithCommasFull (8位小数)
- 已销毁量: 保持 formatIntWithCommas 整数显示不变

贡献值页 (contribution_page.dart) 修改:
- 100亿销毁剩余量: formatAmount(4位) → formatCompactFull (完整精度)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/mining-app/lib/core/utils/format_utils.dart

@@ -44,6 +44,94 @@ String formatWithCommas(String? value) {
   }
 }
 
+/// 将小数点向左移动 [positions] 位（纯字符串操作，不丢精度）
+/// e.g., _shiftDecimalLeft("9813194959.8105", 8) → "98.131949598105"
+String _shiftDecimalLeft(String numStr, int positions) {
+  String sign = '';
+  String v = numStr.trim();
+  if (v.startsWith('-')) {
+    sign = '-';
+    v = v.substring(1);
+  }
+  String intPart, decPart;
+  final dotIndex = v.indexOf('.');
+  if (dotIndex >= 0) {
+    intPart = v.substring(0, dotIndex);
+    decPart = v.substring(dotIndex + 1);
+  } else {
+    intPart = v;
+    decPart = '';
+  }
+  String digits = intPart + decPart;
+  int newDecPos = intPart.length - positions;
+  while (newDecPos <= 0) {
+    digits = '0$digits';
+    newDecPos++;
+  }
+  final newInt = digits.substring(0, newDecPos);
+  var newDec = digits.substring(newDecPos);
+  newDec = newDec.replaceFirst(RegExp(r'0+$'), '');
+  if (newDec.isEmpty) return '$sign$newInt';
+  return '$sign$newInt.$newDec';
+}
+
+/// 整数部分加逗号千位分隔 + 保留原始小数位（纯字符串操作，不丢精度）
+String _addCommasFullPrecision(String numStr) {
+  String sign = '';
+  String v = numStr.trim();
+  if (v.startsWith('-')) {
+    sign = '-';
+    v = v.substring(1);
+  }
+  String intPart, decPart;
+  final dotIndex = v.indexOf('.');
+  if (dotIndex >= 0) {
+    intPart = v.substring(0, dotIndex);
+    decPart = v.substring(dotIndex); // 包含小数点
+  } else {
+    intPart = v;
+    decPart = '';
+  }
+  final formatted = NumberFormat('#,##0', 'zh_CN').format(int.parse(intPart));
+  if (decPart.isNotEmpty) {
+    decPart = decPart.replaceFirst(RegExp(r'0+$'), '');
+    if (decPart == '.') decPart = '';
+  }
+  return '$sign$formatted$decPart';
+}
+
+/// 与 formatCompact 相同的万/亿缩写，但使用字符串小数点移位保留后端返回的全部精度
+String formatCompactFull(String? value) {
+  if (value == null || value.isEmpty) return '0';
+  try {
+    final d = Decimal.parse(value);
+    final abs = d.abs();
+    if (abs >= Decimal.parse('1000000000000')) {
+      return '${_shiftDecimalLeft(value, 12)}万亿';
+    }
+    if (abs >= Decimal.parse('100000000')) {
+      return '${_shiftDecimalLeft(value, 8)}亿';
+    }
+    if (abs >= Decimal.parse('10000')) {
+      return '${_shiftDecimalLeft(value, 4)}万';
+    }
+    return _addCommasFullPrecision(value);
+  } catch (e) {
+    return '0';
+  }
+}
+
+/// 原始数值 + 逗号千位分隔，保留后端返回的全部小数位（不受 double 精度限制）
+String formatWithCommasFull(String? value) {
+  if (value == null || value.isEmpty) return '0';
+  try {
+    Decimal.parse(value); // validate
+    return _addCommasFullPrecision(value);
+  } catch (e) {
+    return '0';
+  }
+}
+
 /// 原始整数 + 逗号千位分隔（不保留小数）
 String formatIntWithCommas(String? value) {
   if (value == null || value.isEmpty) return '0';

frontend/mining-app/lib/presentation/pages/contribution/contribution_page.dart

@@ -231,7 +231,7 @@ class ContributionPage extends ConsumerWidget {
                       hideAmounts
                           ? '******'
                           : market != null
-                              ? formatAmount(
+                              ? formatCompactFull(
                                   (Decimal.parse(market.totalShares) -
                                           Decimal.parse(market.totalMined) -
                                           Decimal.parse(market.blackHoleAmount))

frontend/mining-app/lib/presentation/pages/trading/trading_page.dart

@@ -360,12 +360,11 @@ class _TradingPageState extends ConsumerState<TradingPage> {
               _buildMarketDataItem(
                 '剩余积分股',
                 market != null
-                    ? formatCompact(
+                    ? formatCompactFull(
                         (Decimal.parse(market.totalShares) -
                                 Decimal.parse(market.totalMined) -
                                 Decimal.parse(market.blackHoleAmount))
-                            .toString(),
+                            .toString())
-                        precision: 4)
                     : null,
                 _orange,
                 isLoading,
@@ -376,7 +375,7 @@ class _TradingPageState extends ConsumerState<TradingPage> {
               // 而非交易流通池（circulationPool，目前无交易故为0）
               _buildMarketDataItem(
                 '已分配积分股',
-                market != null ? formatCompact(market.totalMined) : null,
+                market != null ? formatCompactFull(market.totalMined) : null,
                 _orange,
                 isLoading,
               ),
@@ -389,7 +388,7 @@ class _TradingPageState extends ConsumerState<TradingPage> {
             children: [
               _buildMarketDataItem(
                 '积分股池',
-                market != null ? formatWithCommas(market.greenPoints) : null,
+                market != null ? formatWithCommasFull(market.greenPoints) : null,
                 _orange,
                 isLoading,
               ),