Add logs showcase

[bburda]

Summary

Verify and showcase the gateway's /logs endpoint in all demos.

Motivation

Gateway v0.4.0 has a LogManager with configurable log backends. Demos should verify this works and optionally configure log settings.

Proposed solution

• Verify /logs endpoint returns log data in all demos
• Add logs verification to smoke tests
• Optionally: configure log_settings per entity for demo purposes

Acceptance criteria

• Smoke tests verify /logs endpoint returns data in all 3 demos