YouTube Data API v3 engine:
- Add YouTubeConfig to EnginesConfig with api_key field
- Add YOUTUBE_API_KEY env override
- Thread *config.Config through search service to factory
- Factory falls back to env vars if config fields are empty
- Update config.example.toml with youtube section
Also update default local_ported to include google and youtube.
- Rename cmd/searxng-go to cmd/kafka
- Remove all SearXNG references from source comments while keeping
"SearXNG-compatible API" in user-facing docs
- Update binary paths in README, CLAUDE.md, and Dockerfile
- Update log message to "kafka starting"
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
