Initial commit: Backend API Phase 1a complete

- FastAPI backend with JWT auth
- PostgreSQL database schema
- Trees and Sessions CRUD APIs
- Export functionality (Markdown, Text, HTML)
- Docker setup for local development
- Alembic migrations

backend/app/models/team.py

@@ -0,0 +1,25 @@
+import uuid
+from datetime import datetime
+from sqlalchemy import String, DateTime
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from sqlalchemy.dialects.postgresql import UUID
+from app.core.database import Base
+
+
+class Team(Base):
+    __tablename__ = "teams"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        primary_key=True,
+        default=uuid.uuid4
+    )
+    name: Mapped[str] = mapped_column(String(255), nullable=False)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime,
+        default=datetime.utcnow
+    )
+
+    # Relationships
+    users: Mapped[list["User"]] = relationship("User", back_populates="team")
+    trees: Mapped[list["Tree"]] = relationship("Tree", back_populates="team")