feat: 添加批注功能

后端:
- Comment 模型（支持日记/任务/经验三种内容类型）
- CommentSerializer 和 CommentViewSet
- API: /api/comments/ - 批注 CRUD
- API: /api/comments/by_content/?content_type=diary&object_id=1 - 按内容获取批注
- 日记/任务/经验序列化器嵌套显示批注

前端:
- 批注样式（comments-section, comment-item）
- 添加批注输入框

使用方式:
- 北极星可以在任何日记/任务/经验下添加批注
- 批注会显示在内容下方
- 支持查看历史批注

backend/diary/migrations/0005_comment.py

@@ -0,0 +1,29 @@
+# Generated by Django 4.2.11 on 2026-04-14 11:45
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('diary', '0004_diaryentry_content_diaryentry_linked_tasks_and_more'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Comment',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('content_type', models.CharField(choices=[('diary', '日记'), ('task', '任务'), ('experience', '经验')], max_length=20, verbose_name='内容类型')),
+                ('object_id', models.IntegerField(verbose_name='内容 ID')),
+                ('content', models.TextField(verbose_name='批注内容')),
+                ('created_by', models.CharField(default='北极星', max_length=100, verbose_name='创建者')),
+                ('created_at', models.DateTimeField(auto_now_add=True, verbose_name='创建时间')),
+            ],
+            options={
+                'verbose_name': '批注',
+                'verbose_name_plural': '批注',
+                'ordering': ['-created_at'],
+            },
+        ),
+    ]

backend/diary/models.py

@@ -93,6 +93,29 @@ class DailyProgress(models.Model):
         return f"{self.entry.date} - {self.category}: {self.progress_percent}%"
 
 
+class Comment(models.Model):
+    """批注 - 用户可以对日记/任务/经验添加评论"""
+    CONTENT_TYPE_CHOICES = [
+        ('diary', '日记'),
+        ('task', '任务'),
+        ('experience', '经验'),
+    ]
+
+    content_type = models.CharField('内容类型', max_length=20, choices=CONTENT_TYPE_CHOICES)
+    object_id = models.IntegerField('内容 ID')
+    content = models.TextField('批注内容')
+    created_by = models.CharField('创建者', max_length=100, default='北极星')
+    created_at = models.DateTimeField('创建时间', auto_now_add=True)
+
+    class Meta:
+        ordering = ['-created_at']
+        verbose_name = '批注'
+        verbose_name_plural = '批注'
+
+    def __str__(self):
+        return f"{self.content_type} #{self.object_id} - {self.created_by}"
+
+
 class Task(models.Model):
     """工作任务 - 跟踪任务和进展"""
     STATUS_CHOICES = [

backend/diary/serializers.py

@@ -1,8 +1,15 @@
 from rest_framework import serializers
-from .models import DiaryEntry, DailyProgress, Experience, Task
+from .models import DiaryEntry, DailyProgress, Experience, Task, Comment
+
+class CommentSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = Comment
+        fields = '__all__'
+        read_only_fields = ['created_at']
 
 class ExperienceSerializer(serializers.ModelSerializer):
     category_display = serializers.CharField(source='get_category_display', read_only=True)
+    comments = CommentSerializer(many=True, read_only=True, source='comment_set')
     
     class Meta:
         model = Experience
@@ -24,6 +31,7 @@ class DiaryEntrySerializer(serializers.ModelSerializer):
     progresses = DailyProgressSerializer(many=True, read_only=True)
     linked_tasks = TaskSimpleSerializer(many=True, read_only=True)
     experiences = ExperienceSerializer(many=True, read_only=True)
+    comments = CommentSerializer(many=True, read_only=True, source='comment_set')
     
     class Meta:
         model = DiaryEntry
@@ -33,9 +41,10 @@ class TaskSerializer(serializers.ModelSerializer):
     status_display = serializers.CharField(source='get_status_display', read_only=True)
     priority_display = serializers.CharField(source='get_priority_display', read_only=True)
     diary_entries = serializers.SerializerMethodField()
+    comments = CommentSerializer(many=True, read_only=True, source='comment_set')
     
     def get_diary_entries(self, obj):
-        entries = obj.diary_entries.all()[:5]  # 最近 5 条关联日记
+        entries = obj.diary_entries.all()[:5]
         return DiaryEntrySerializer(entries, many=True).data
 
     class Meta:

backend/diary/urls.py

@@ -1,12 +1,13 @@
 from django.urls import path, include
 from rest_framework.routers import DefaultRouter
-from .views import DiaryEntryViewSet, DailyProgressViewSet, ExperienceViewSet, TaskViewSet
+from .views import DiaryEntryViewSet, DailyProgressViewSet, ExperienceViewSet, TaskViewSet, CommentViewSet
 
 router = DefaultRouter()
 router.register(r'entries', DiaryEntryViewSet)
 router.register(r'progress', DailyProgressViewSet)
 router.register(r'experiences', ExperienceViewSet)
 router.register(r'tasks', TaskViewSet)
+router.register(r'comments', CommentViewSet)
 
 urlpatterns = [
     path('', include(router.urls)),

backend/diary/views.py

@@ -2,8 +2,11 @@ from rest_framework import viewsets
 from rest_framework.decorators import action
 from rest_framework.response import Response
 from django.utils import timezone
-from .models import DiaryEntry, DailyProgress, Experience, Task
-from .serializers import DiaryEntrySerializer, DailyProgressSerializer, ExperienceSerializer, TaskSerializer
+from .models import DiaryEntry, DailyProgress, Experience, Task, Comment
+from .serializers import (
+    DiaryEntrySerializer, DailyProgressSerializer, ExperienceSerializer,
+    TaskSerializer, CommentSerializer
+)
 
 class DiaryEntryViewSet(viewsets.ModelViewSet):
     queryset = DiaryEntry.objects.all()
@@ -146,3 +149,24 @@ class TaskViewSet(viewsets.ModelViewSet):
         task = self.get_object()
         task.mark_completed()
         return Response(TaskSerializer(task).data)
+
+
+class CommentViewSet(viewsets.ModelViewSet):
+    queryset = Comment.objects.all()
+    serializer_class = CommentSerializer
+
+    @action(detail=False, methods=['get'])
+    def by_content(self, request):
+        """按内容类型和 ID 获取批注"""
+        content_type = request.query_params.get('content_type')
+        object_id = request.query_params.get('object_id')
+        
+        if content_type and object_id:
+            comments = Comment.objects.filter(
+                content_type=content_type,
+                object_id=object_id
+            )
+            serializer = self.get_serializer(comments, many=True)
+            return Response(serializer.data)
+        
+        return Response([])