Refactor controllers for better readability

**Description**
Currently handlers lacks proper serialization support.

**Proposed solution**
Add configurable serialization with sensible defaults.

**Priority**: Low/Medium

No files, tests, or entry points are named. Start by locating the controllers and handlers, then inspect how their responses are currently serialized and whether configuration already exists. Define the expected configurable options and defaults with the maintainer, and add coverage showing the chosen serialization behavior.

Written by the indexing model from the issue text.