feat: 接入起卦后端流程并完善积分扣减链路

apps/lib/features/settings/presentation/screens/legal_document_screen.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_markdown/flutter_markdown.dart';
 
+import '../../../../l10n/app_localizations.dart';
 import '../../../../shared/theme/design_tokens.dart';
 import '../../../../shared/widgets/app_loading_indicator.dart';
 
@@ -15,9 +16,23 @@ class LegalDocumentScreen extends StatelessWidget {
   final String title;
   final String assetPath;
 
+  Future<String> _loadAsset() async {
+    try {
+      final data = await rootBundle.loadString(assetPath);
+      if (data.isEmpty) {
+        throw Exception('Asset file is empty: $assetPath');
+      }
+      return data;
+    } catch (e) {
+      debugPrint('Failed to load asset: $assetPath, error: $e');
+      rethrow;
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
     final colors = Theme.of(context).colorScheme;
+    final l10n = AppLocalizations.of(context)!;
     return Scaffold(
       backgroundColor: colors.surfaceContainerLow,
       appBar: AppBar(
@@ -27,8 +42,43 @@ class LegalDocumentScreen extends StatelessWidget {
         surfaceTintColor: colors.surfaceContainerLow,
       ),
       body: FutureBuilder<String>(
-        future: rootBundle.loadString(assetPath),
+        future: _loadAsset(),
         builder: (context, snapshot) {
+          if (snapshot.hasError) {
+            return Center(
+              child: Padding(
+                padding: const EdgeInsets.all(AppSpacing.lg),
+                child: Column(
+                  mainAxisAlignment: MainAxisAlignment.center,
+                  children: [
+                    Icon(Icons.error_outline, size: 48, color: colors.error),
+                    const SizedBox(height: AppSpacing.md),
+                    Text(
+                      l10n.legalDocumentLoadFailedTitle,
+                      style: Theme.of(context).textTheme.titleMedium,
+                    ),
+                    const SizedBox(height: AppSpacing.sm),
+                    Text(
+                      '${l10n.legalDocumentLoadFailedPathPrefix}: $assetPath',
+                      style: Theme.of(
+                        context,
+                      ).textTheme.bodySmall?.copyWith(color: colors.error),
+                      textAlign: TextAlign.center,
+                    ),
+                    const SizedBox(height: AppSpacing.xs),
+                    Text(
+                      '${l10n.legalDocumentLoadFailedErrorPrefix}: ${snapshot.error}',
+                      style: Theme.of(
+                        context,
+                      ).textTheme.bodySmall?.copyWith(color: colors.error),
+                      textAlign: TextAlign.center,
+                    ),
+                  ],
+                ),
+              ),
+            );
+          }
+
           if (!snapshot.hasData) {
             return const Center(
               child: AppLoadingIndicator(variant: AppLoadingVariant.surface),