feat(C-06)：关注feed+课程聚合修复

文章列表新增author_user_id/is_following与feed=following过滤；课程students_count改真实在学人数去重统计、新增total_minutes（不可解析不伪造）；author_name走sync_to_async防ASGI同步阻塞。

learn/serializers.py

@@ -1,9 +1,67 @@
 from adrf.serializers import (
     ModelSerializer, SerializerMethodField,
 )
+from asgiref.sync import sync_to_async
+
 from .models import Course, Chapter, ChapterContent, CourseMaterial
 
 
+def _author_display(obj):
+    """同步取作者展示名（跑在 sync_to_async 线程里，避免 ASGI 下 SynchronousOnlyOperation）。"""
+    try:
+        author = obj.author
+    except Exception:
+        return ''
+    if author is None:
+        return ''
+    try:
+        full = author.get_full_name()
+    except Exception:
+        full = ''
+    try:
+        username = author.username
+    except Exception:
+        username = ''
+    return full or username or ''
+
+
+def parse_duration_minutes(raw):
+    """把章节 duration 字符串解析为分钟数；解析不出返回 None。
+
+    存量格式为中文字符串（如 '30分钟'），纯数字视为分钟。
+    total_minutes 只对可解析章节求和，不可解析章节不计入（不伪造）。
+    """
+    import re
+    if raw is None:
+        return None
+    s = str(raw).strip()
+    if not s:
+        return None
+    m = re.search(r'(\d+(?:\.\d+)?)', s)
+    if not m:
+        return None
+    try:
+        return int(float(m.group(1)))
+    except (ValueError, OverflowError):
+        return None
+
+
+def _course_total_minutes(obj):
+    """同步聚合课程总分钟数（跑在 sync_to_async 线程里）。"""
+    try:
+        durations = list(obj.chapters.values_list('duration', flat=True))
+    except Exception:
+        return None
+    total = 0
+    any_parsed = False
+    for d in durations:
+        m = parse_duration_minutes(d)
+        if m is not None:
+            total += m
+            any_parsed = True
+    return total if any_parsed else None
+
+
 class ChapterSerializer(ModelSerializer):
     video_poster_url = SerializerMethodField()
     video_local_url = SerializerMethodField()
@@ -100,6 +158,7 @@ class CourseListSerializer(ModelSerializer):
     author_name = SerializerMethodField()
     chapters_count = SerializerMethodField()
     students_count = SerializerMethodField()
+    total_minutes = SerializerMethodField()
     cover_image_url = SerializerMethodField()
 
     class Meta:
@@ -107,7 +166,7 @@ class CourseListSerializer(ModelSerializer):
         fields = [
             'id', 'title', 'description', 'category', 'level',
             'cover_image_url', 'color', 'icon_name', 'author_name',
-            'chapters_count', 'students_count', 'status',
+            'chapters_count', 'students_count', 'total_minutes', 'status',
             'sort_order', 'is_hot', 'is_new', 'created_at', 'updated_at',
         ]
 
@@ -115,7 +174,15 @@ class CourseListSerializer(ModelSerializer):
         return await obj.chapters.acount()
 
     async def get_students_count(self, obj):
-        return 0
+        # 从章节阅读记录去重统计真实在学人数
+        from user.models import FUser
+        return await FUser.objects.filter(
+            chapter_reads__course=obj
+        ).distinct().acount()
+
+    async def get_total_minutes(self, obj):
+        # 可解析章节 duration 求和；全不可解析返回 None（前端不显示，不伪造）
+        return await sync_to_async(_course_total_minutes)(obj)
 
     async def get_cover_image_url(self, obj):
         if obj.cover_image:
@@ -126,9 +193,7 @@ class CourseListSerializer(ModelSerializer):
         return ''
 
     async def get_author_name(self, obj):
-        if obj.author:
-            return obj.author.get_full_name() or obj.author.username
-        return ''
+        return await sync_to_async(_author_display)(obj)
 
 
 class CourseDetailSerializer(ModelSerializer):
@@ -136,6 +201,7 @@ class CourseDetailSerializer(ModelSerializer):
     chapters = ChapterSerializer(many=True, read_only=True)
     chapters_count = SerializerMethodField()
     students_count = SerializerMethodField()
+    total_minutes = SerializerMethodField()
     cover_image_url = SerializerMethodField()
 
     class Meta:
@@ -143,7 +209,7 @@ class CourseDetailSerializer(ModelSerializer):
         fields = [
             'id', 'title', 'description', 'category', 'level',
             'cover_image_url', 'color', 'icon_name', 'author_name',
-            'chapters', 'chapters_count', 'students_count', 'status',
+            'chapters', 'chapters_count', 'students_count', 'total_minutes', 'status',
             'sort_order', 'is_hot', 'is_new', 'created_at', 'updated_at',
         ]
 
@@ -151,7 +217,14 @@ class CourseDetailSerializer(ModelSerializer):
         return await obj.chapters.acount()
 
     async def get_students_count(self, obj):
-        return 0
+        # 从章节阅读记录去重统计真实在学人数
+        from user.models import FUser
+        return await FUser.objects.filter(
+            chapter_reads__course=obj
+        ).distinct().acount()
+
+    async def get_total_minutes(self, obj):
+        return await sync_to_async(_course_total_minutes)(obj)
 
     async def get_cover_image_url(self, obj):
         if obj.cover_image:
@@ -162,9 +235,7 @@ class CourseDetailSerializer(ModelSerializer):
         return ''
 
     async def get_author_name(self, obj):
-        if obj.author:
-            return obj.author.get_full_name() or obj.author.username
-        return ''
+        return await sync_to_async(_author_display)(obj)
 
 
 class CourseCreateUpdateSerializer(ModelSerializer):