Various fixes

folkugat_web/model/sessions.py

@@ -6,13 +6,13 @@ DEFAULT_START_TIME = datetime.time(20, 30)
 DEFAULT_END_TIME = datetime.time(22, 30)
 
 
-@dataclasses.dataclass
+@dataclasses.dataclass(frozen=True)
 class SessionVenue:
     name: str | None = None
     url: str | None = None
 
 
-@dataclasses.dataclass
+@dataclasses.dataclass(frozen=True)
 class Session:
     id: int | None = None
     date: datetime.date = dataclasses.field(default_factory=datetime.date.today)