chore: 将后端移动到 api/ 目录，准备合并为单仓库

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

api/prompt/models.py

@@ -0,0 +1,47 @@
+import uuid
+from django.db import models
+from django_extensions.db.models import TimeStampedModel
+from account.models import User
+from task.models import Task
+
+
+class Conversation(TimeStampedModel):
+    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name="conversations")
+    task = models.ForeignKey(Task, on_delete=models.CASCADE, related_name="conversations")
+    is_active = models.BooleanField(default=True, verbose_name="是否活跃")
+
+    class Meta:
+        ordering = ("-created",)
+
+    def __str__(self):
+        return f"{self.user.username} - {self.task.title}"
+
+
+class Message(models.Model):
+    conversation = models.ForeignKey(
+        Conversation, on_delete=models.CASCADE, related_name="messages"
+    )
+    role = models.CharField(max_length=10)  # "user" or "assistant"
+    source = models.CharField(max_length=12, default="conversation")  # "conversation" or "manual"
+    content = models.TextField()
+    code_html = models.TextField(null=True, blank=True)
+    code_css = models.TextField(null=True, blank=True)
+    code_js = models.TextField(null=True, blank=True)
+    created = models.DateTimeField(auto_now_add=True)
+    prompt_level = models.IntegerField(
+        null=True, blank=True, default=None, db_index=True, verbose_name="提示词层级"
+    )
+    submission = models.OneToOneField(
+        "submission.Submission",
+        null=True,
+        blank=True,
+        on_delete=models.CASCADE,
+        related_name="source_message",
+    )
+
+    class Meta:
+        ordering = ("created",)
+
+    def __str__(self):
+        return f"[{self.role}] {self.content[:50]}"