Add FastAPI backend with agent system

backend/app/models/__init__.py

@@ -0,0 +1,31 @@
+from app.models.base import Base
+from app.models.user import User
+from app.models.document import Document, DocumentChunk
+from app.models.task import Task, TaskHistory
+from app.models.forum import ForumPost, ForumReply
+from app.models.agent import Agent, AgentMessage
+from app.models.conversation import Conversation, Message
+from app.models.knowledge_graph import KGNode, KGEdge
+from app.models.memory import MemorySummary, UserMemory
+from app.models.todo import DailyTodo, TodoSource
+
+__all__ = [
+    "Base",
+    "User",
+    "Document",
+    "DocumentChunk",
+    "Task",
+    "TaskHistory",
+    "ForumPost",
+    "ForumReply",
+    "Agent",
+    "AgentMessage",
+    "Conversation",
+    "Message",
+    "KGNode",
+    "KGEdge",
+    "MemorySummary",
+    "UserMemory",
+    "DailyTodo",
+    "TodoSource",
+]