feat(app): 内容安全词库 + 过滤服务 + 分享前检查 — 28 个测试全覆盖

新增文件：
- sensitive_words.dart — 8 分类 ~200 条敏感词 + 谐音/形近/数字变体映射
- content_filter_service.dart — 精确匹配 + 变体匹配 + 文本预处理（去零宽/空格/符号）
- content_filter_service_test.dart — 28 个测试（8分类精确/安全内容/预处理/变体/边界/词库完整性）

修改：
- share_bottom_sheet.dart — 分享到班级前调用 ContentFilterService，
  有敏感词时弹出警告对话框（返回修改/仍然分享），新增 contentText 参数

app/lib/features/editor/widgets/share_bottom_sheet.dart

@@ -4,20 +4,27 @@
 // - 温暖友好的文案（面向小学生）
 // - 分享到班级（有班级时显示）/ 仅自己可见
 // - 无班级时提示加入班级后可分享
+// - 分享前自动进行内容安全检查（敏感词过滤）
 
 import 'package:flutter/material.dart';
 
+import '../../../data/services/content_filter_service.dart';
+
 /// 编辑器完成后的分享选择面板
 class ShareBottomSheet extends StatelessWidget {
   final String? classId;
   final String className;
   final void Function(bool shareToClass) onDecision;
 
+  /// 用于内容安全检查的文本内容（标题 + 文本元素）
+  final String contentText;
+
   const ShareBottomSheet({
     super.key,
     required this.classId,
     required this.className,
     required this.onDecision,
+    this.contentText = '',
   });
 
   @override
@@ -65,10 +72,7 @@ class ShareBottomSheet extends StatelessWidget {
               width: double.infinity,
               height: 52,
               child: FilledButton.icon(
-                onPressed: () {
-                  onDecision(true);
-                  Navigator.pop(context);
-                },
+                onPressed: () => _handleShare(context, shareToClass: true),
                 icon: const Icon(Icons.group),
                 label: Text('分享到 $className'),
                 style: FilledButton.styleFrom(
@@ -86,10 +90,7 @@ class ShareBottomSheet extends StatelessWidget {
             width: double.infinity,
             height: 52,
             child: OutlinedButton.icon(
-              onPressed: () {
-                onDecision(false);
-                Navigator.pop(context);
-              },
+              onPressed: () => _handleShare(context, shareToClass: false),
               icon: const Icon(Icons.lock_outline),
               label: const Text('仅自己可见'),
               style: OutlinedButton.styleFrom(
@@ -116,4 +117,80 @@ class ShareBottomSheet extends StatelessWidget {
       ),
     );
   }
+
+  /// 处理分享/保存决定
+  void _handleShare(BuildContext context, {required bool shareToClass}) {
+    // 仅在分享到班级时进行内容安全检查
+    if (shareToClass && contentText.isNotEmpty) {
+      final matches = ContentFilterService.checkText(contentText);
+      if (matches.isNotEmpty) {
+        _showContentWarning(context, matches);
+        return;
+      }
+    }
+    // 安全或仅自己可见 → 直接执行
+    onDecision(shareToClass);
+    Navigator.pop(context);
+  }
+
+  /// 显示内容安全警告对话框
+  void _showContentWarning(
+    BuildContext context,
+    List<SensitiveWordMatch> matches,
+  ) {
+    final categories = ContentFilterService.getMatchedCategories(matches);
+    final words = matches.map((m) => ' "${m.word}"').toSet().toList();
+    final wordList = words.take(5).join('、');
+    final categoryList = categories.join('、');
+
+    showDialog(
+      context: context,
+      builder: (dialogContext) => AlertDialog(
+        shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(16)),
+        title: const Row(
+          children: [
+            Icon(Icons.warning_amber_rounded, color: Colors.orange),
+            SizedBox(width: 8),
+            Text('内容提醒'),
+          ],
+        ),
+        content: Column(
+          mainAxisSize: MainAxisSize.min,
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: [
+            const Text('日记中可能包含不太合适分享的内容：'),
+            const SizedBox(height: 8),
+            Text(
+              wordList,
+              style: const TextStyle(fontWeight: FontWeight.w600),
+            ),
+            const SizedBox(height: 4),
+            Text(
+              '涉及：$categoryList',
+              style: TextStyle(fontSize: 13, color: Colors.grey.shade600),
+            ),
+            const SizedBox(height: 12),
+            const Text(
+              '建议修改后再分享，或者先保存为仅自己可见。',
+              style: TextStyle(fontSize: 13),
+            ),
+          ],
+        ),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.pop(dialogContext),
+            child: const Text('返回修改'),
+          ),
+          TextButton(
+            onPressed: () {
+              Navigator.pop(dialogContext); // 关闭对话框
+              onDecision(true); // 仍然分享
+              Navigator.pop(context); // 关闭 BottomSheet
+            },
+            child: const Text('仍然分享'),
+          ),
+        ],
+      ),
+    );
+  }
 }