Add FastAPI backend with agent system

backend/app/models/forum.py

@@ -0,0 +1,30 @@
+from sqlalchemy import Column, String, Text, Integer, ForeignKey, Boolean
+from sqlalchemy.orm import relationship
+from app.models.base import BaseModel
+
+
+class ForumPost(BaseModel):
+    __tablename__ = "forum_posts"
+
+    user_id = Column(String(36), ForeignKey("users.id"), nullable=False, index=True)
+    title = Column(String(500), nullable=False)
+    content = Column(Text, nullable=False)
+    category = Column(String(100), nullable=True)  # instruction, discussion, question
+    is_executed = Column(Boolean, default=False)
+    execution_result = Column(Text, nullable=True)
+    reply_count = Column(Integer, default=0)
+
+    replies = relationship("ForumReply", back_populates="post", cascade="all, delete-orphan")
+
+
+class ForumReply(BaseModel):
+    __tablename__ = "forum_replies"
+
+    post_id = Column(String(36), ForeignKey("forum_posts.id"), nullable=False, index=True)
+    user_id = Column(String(36), ForeignKey("users.id"), nullable=True)
+    agent_id = Column(String(36), ForeignKey("agents.id"), nullable=True)
+    content = Column(Text, nullable=False)
+    is_ai_reply = Column(Boolean, default=False)
+
+    post = relationship("ForumPost", back_populates="replies")
+    agent = relationship("Agent", back_populates="replies")