Optimize middleware for large datasets

**Description**
Currently api 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 API middleware and its current serialization path, then determine the required configuration surface and sensible defaults. Done means configurable serialization support is implemented and verified for large datasets.

Written by the indexing model from the issue text.