feat: add operator landing and login

backend/app/schemas/auth.py

@@ -0,0 +1,23 @@
+from __future__ import annotations
+
+from datetime import datetime
+
+from pydantic import BaseModel, Field
+
+from app.schemas.common import Envelope
+
+
+class AuthLoginRequest(BaseModel):
+    username: str = Field(min_length=1, max_length=128)
+    password: str = Field(min_length=1, max_length=1024)
+
+
+class AuthSession(BaseModel):
+    authentication_required: bool
+    authenticated: bool
+    username: str | None = None
+    expires_at: datetime | None = None
+
+
+class AuthSessionEnvelope(Envelope[AuthSession]):
+    pass