Adds user settings for the Castle extension

Adds functionality to configure the Castle extension, including a wallet ID.

This allows administrators to customize the extension's behavior by specifying a dedicated wallet for castle operations.

models.py

@@ -102,3 +102,20 @@ class RevenueEntry(BaseModel):
     payment_method_account: str  # e.g., "Cash", "Bank", "Lightning"
     reference: Optional[str] = None
     currency: Optional[str] = None  # If None, amount is in satoshis. Otherwise, fiat currency code
+
+
+class CastleSettings(BaseModel):
+    """Settings for the Castle extension"""
+
+    castle_wallet_id: Optional[str] = None  # The wallet ID that represents the Castle
+    updated_at: datetime = Field(default_factory=lambda: datetime.now())
+
+    @classmethod
+    def is_admin_only(cls) -> bool:
+        return True
+
+
+class UserCastleSettings(CastleSettings):
+    """User-specific settings (stored with user_id)"""
+
+    id: str