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/admin.py

@@ -0,0 +1,15 @@
+from django.contrib import admin
+from .models import Conversation, Message
+
+
+class MessageInline(admin.TabularInline):
+    model = Message
+    extra = 0
+    readonly_fields = ("role", "content", "code_html", "code_css", "code_js", "created")
+
+
+@admin.register(Conversation)
+class ConversationAdmin(admin.ModelAdmin):
+    list_display = ("user", "task", "is_active", "created")
+    list_filter = ("is_active",)
+    inlines = [MessageInline]