Gateway: Add SOVD bulk-data endpoints and fault detail response

[bburda]

Summary

Expose rosbag recordings captured by the fault manager through SOVD-compliant REST endpoints, and add a proper fault detail response with environment data.

Currently the gateway has no way to:

1. List and download rosbag files recorded during faults
2. Return fault detail with environment data (freeze frames, timestamps, rosbag references)
3. Batch-retrieve rosbag metadata without N+1 service calls

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Proposed solution

SOVD Bulk-Data Endpoints

Implement the three SOVD bulk-data endpoints for all entity types:

• GET /{entity_type}/{id}/bulk-data — list categories (currently: rosbags)
• GET /{entity_type}/{id}/bulk-data/rosbags — list available rosbag recordings with metadata
• GET /{entity_type}/{id}/bulk-data/rosbags/{descriptor_id} — download rosbag file

Download must use chunked streaming (httplib::set_content_provider with 64KB chunks) since rosbag files can be hundreds of MB to multiple GB.