Use `DTO`s for Controllers

[Anikate-De]

Returning Domain level Models is bad. Really bad.

So bad that GPT4 says:

1. Leaky Abstraction: Returning entities exposes the internal structure of the database, leading to a tightly coupled design, making it harder to change the schema without breaking the API.
2. Security Risks: Entities might contain sensitive data that could accidentally be exposed, even with @JsonIgnore, increasing the risk of data leakage.
3. Performance Overhead: Entities often include unnecessary fields and relationships, which may result in over-fetching data that is irrelevant for the client, leading to inefficiency.
4. Serialization Issues: Entities might have complex relationships (e.g., bidirectional associations) that can lead to infinite loops during serialization, even with @JsonIgnore.
5. Separation of Concerns: Using DTOs ensures that the API layer is separated from the persistence layer, promoting cleaner code and reducing unintended side effects during data transformation.