Add validation for god names in application

[moller2866]

Problem:
There is currently no validation enforcing acceptable god names within the application. This could lead to inconsistencies, invalid data, or possible misuse of the system.

Steps to Implement:

1. Define what constitutes a valid god name (for example: required fields, allowed characters, maximum length, allowed/forbidden list, uniqueness).
2. Update the data model and/or DTOs to enforce these validation rules in the backend code (likely in C#).
3. Add validation logic in the relevant C# service, model, or API controller (e.g., using data annotation attributes or business logic).
4. Update any user input forms or API endpoints to provide useful validation feedback/messages to clients when invalid god names are submitted.
5. Add unit and/or integration tests to verify correct handling of both valid and invalid god names through the API and, if applicable, the UI.
6. (Optional) Document allowed values/rules for god names in API or user documentation (e.g., README or OpenAPI schema).

Implementation Hints:

• Most of the application is written in C#. Implement the validation in the appropriate C# class or service layer responsible for managing gods data.
• Consider how validation errors are returned to clients (e.g., error codes, messages).
• Update database constraints if required.

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Repo language breakdown: C# (90%), Bicep (9.1%), Dockerfile (0.9%)