Initial MVP skeleton with auth, chat persistence, UI and text LLM integration

backend/app/db/models.py

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+from datetime import datetime, timezone
+import uuid
+
+from sqlalchemy import Column, String, Boolean, DateTime, ForeignKey, Text
+from sqlalchemy.orm import relationship
+
+from app.db.base_class import Base
+
+def generate_uuid() -> str:
+    return uuid.uuid4().hex
+
+def utc_now() -> datetime:
+    return datetime.now(timezone.utc).replace(tzinfo=None)
+
+class User(Base):
+    __tablename__ = "users"
+
+    id = Column(String, primary_key=True, index=True, default=generate_uuid)
+    login = Column(String, unique=True, index=True, nullable=False)
+    hashed_password = Column(String, nullable=False)
+    is_active = Column(Boolean, default=True)
+
+    sessions = relationship("Session", back_populates="user", cascade="all, delete-orphan")
+    chats = relationship("Chat", back_populates="user", cascade="all, delete-orphan")
+
+class Session(Base):
+    __tablename__ = "sessions"
+
+    id = Column(String, primary_key=True, index=True, default=generate_uuid)
+    user_id = Column(String, ForeignKey("users.id"), nullable=False, index=True)
+    expires_at = Column(DateTime, nullable=False)
+
+    user = relationship("User", back_populates="sessions")
+
+class Chat(Base):
+    __tablename__ = "chats"
+
+    id = Column(String, primary_key=True, index=True, default=generate_uuid)
+    user_id = Column(String, ForeignKey("users.id"), nullable=False, index=True)
+    title = Column(String, nullable=False, default="New Chat")
+    model_alias = Column(String, nullable=False)
+    created_at = Column(DateTime, nullable=False, default=utc_now)
+    updated_at = Column(DateTime, nullable=False, default=utc_now, onupdate=utc_now)
+
+    user = relationship("User", back_populates="chats")
+    messages = relationship("Message", back_populates="chat", cascade="all, delete-orphan", order_by="Message.created_at")
+
+class Message(Base):
+    __tablename__ = "messages"
+
+    id = Column(String, primary_key=True, index=True, default=generate_uuid)
+    chat_id = Column(String, ForeignKey("chats.id"), nullable=False, index=True)
+    role = Column(String, nullable=False)  # system, user, assistant
+    content = Column(Text, nullable=False)
+    created_at = Column(DateTime, nullable=False, default=utc_now)
+
+    chat = relationship("Chat", back_populates="messages")
+    attachments = relationship("Attachment", back_populates="message", cascade="all, delete-orphan")
+
+class Attachment(Base):
+    __tablename__ = "attachments"
+
+    id = Column(String, primary_key=True, index=True, default=generate_uuid)
+    message_id = Column(String, ForeignKey("messages.id"), nullable=False, index=True)
+    filename = Column(String, nullable=False)
+    content_type = Column(String, nullable=False)
+    file_path = Column(String, nullable=False)
+    created_at = Column(DateTime, nullable=False, default=utc_now)
+
+    message = relationship("Message", back_populates="attachments")