feat(avatar): add private vision chat support

digital-avatar-app/backend/models.py

@@ -257,6 +257,44 @@ class KnowledgeChunk(Base):
         }
 
 
+class ChatAttachment(Base):
+    """Private, avatar-scoped result of one chat image analysis."""
+
+    __tablename__ = "chat_attachments"
+    id = Column(String, primary_key=True, default=lambda: uuid.uuid4().hex)
+    avatar_id = Column(String, nullable=False, default="", index=True)
+    uploader_kind = Column(String, default="owner")  # owner | public
+    filename = Column(String, default="")
+    mime_type = Column(String, default="")
+    file_size = Column(Integer, default=0)
+    status = Column(String, default="processing")  # processing | ready | failed
+    category = Column(String, default="general_image")
+    summary = Column(Text, default="")
+    extracted_text = Column(Text, default="")
+    structured_data = Column(JSON, default=dict)
+    warning = Column(Text, default="")
+    vision_model = Column(String, default="")
+    ocr_model = Column(String, default="")
+    used_at = Column(DateTime)
+    expires_at = Column(DateTime, nullable=False)
+    created_at = Column(DateTime, server_default=func.now())
+
+    def to_dict(self):
+        return {
+            "id": self.id,
+            "avatarId": self.avatar_id,
+            "filename": self.filename,
+            "mimeType": self.mime_type,
+            "fileSize": self.file_size,
+            "status": self.status,
+            "category": self.category,
+            "summary": self.summary,
+            "warning": self.warning,
+            "expiresAt": _iso(self.expires_at),
+            "createdAt": _iso(self.created_at),
+        }
+
+
 class TokenAccount(Base):
     __tablename__ = "token_account"
     id = Column(Integer, primary_key=True)