add social interactions, rich media metadata, and workspace description

app/models/interaction.py

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+from sqlalchemy import Column, DateTime, String, ForeignKey, UniqueConstraint
+from sqlalchemy.sql import func
+from .base import AutoID, Base
+
+class ProjectLike(Base, AutoID):
+    """项目点赞表"""
+    __tablename__ = "project_likes"
+
+    user_id = Column(String(32), ForeignKey("users.id", ondelete="CASCADE"), index=True)
+    project_node_id = Column(String(32), ForeignKey("project_nodes.id", ondelete="CASCADE"), index=True)
+    
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    # 联合唯一约束，防止同一用户重复点赞
+    __table_args__ = (UniqueConstraint("user_id", "project_node_id", name="uq_user_project_like"),)
+
+
+class ProjectFavorite(Base, AutoID):
+    """项目收藏表"""
+    __tablename__ = "project_favorites"
+
+    user_id = Column(String(32), ForeignKey("users.id", ondelete="CASCADE"), index=True)
+    project_node_id = Column(String(32), ForeignKey("project_nodes.id", ondelete="CASCADE"), index=True)
+    
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    # 联合唯一约束，防止重复收藏
+    __table_args__ = (UniqueConstraint("user_id", "project_node_id", name="uq_user_project_favorite"),)
+
+
+class ProjectShare(Base, AutoID):
+    """项目转发/分享记录表"""
+    __tablename__ = "project_shares"
+
+    user_id = Column(String(32), ForeignKey("users.id", ondelete="CASCADE"), index=True)
+    project_node_id = Column(String(32), ForeignKey("project_nodes.id", ondelete="CASCADE"), index=True)
+    
+    # 转发去向或渠道，例如 'internal' (转发到其他工作区), 'twitter', 'link' (复制链接)
+    share_target = Column(String, default="internal", nullable=False)
+    
+    # 如果是转发到特定工作区，可以记录目标工作区 ID
+    target_workspace_id = Column(String(32), ForeignKey("workspaces.id", ondelete="SET NULL"), nullable=True)
+
+    created_at = Column(DateTime(timezone=True), server_default=func.now())