feat: authentication — register, login, JWT, tests

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/schemas/user.py

@@ -0,0 +1,33 @@
+import uuid
+from datetime import datetime
+
+from pydantic import BaseModel, EmailStr
+
+from app.models.user import UserRole
+
+
+class UserCreate(BaseModel):
+    username: str
+    email: str
+    password: str
+
+
+class UserLogin(BaseModel):
+    username: str
+    password: str
+
+
+class UserResponse(BaseModel):
+    id: uuid.UUID
+    username: str
+    email: str
+    role: UserRole
+    is_active: bool
+    created_at: datetime
+
+    model_config = {"from_attributes": True}
+
+
+class Token(BaseModel):
+    access_token: str
+    token_type: str = "bearer"