feat: configure Kanban login with optional email

local/models.py

@@ -88,9 +88,17 @@ class Login(StrictModel):
     password: str = Field(min_length=1, max_length=128)
 
 class OperatorLogin(StrictModel):
-    username: str = Field(min_length=1, max_length=100)
+    email: str = Field(min_length=3, max_length=254)
     password: str = Field(min_length=1, max_length=128)
 
+    @field_validator('email')
+    @classmethod
+    def operator_email_valid(cls, value):
+        value = value.strip().lower()
+        if not re.fullmatch(r'[^\s@]+@[^\s@]+\.[a-zA-Z]{2,}', value):
+            raise ValueError('Invalid email')
+        return value
+
 class FileReference(StrictModel):
     upload_id: UUID
     item_index: int = Field(ge=0, strict=True)