fix: persist environment selection, support Kilo AI provider, resolve Superset virtual columns for translation preview

- Add environment_id to TranslationJob model/schema/API + DB migration
- Pass environmentId from page to TranslationPreview and fetchPreview
- Fix _fetch_sample_rows: use result_type='samples' to include virtual cols
- Add 'kilo' and 'openrouter' to supported LLM provider types
- Make response_format conditional (skip for non-OpenAI upstream providers)
- Remove source_table field from form (redundant with datasource)
- Restore datasourceSearch display from saved job on page load
- Add request/response logging for LLM API calls

backend/src/api/routes/translate/_preview_routes.py

@@ -52,6 +52,7 @@ async def preview_translation(
             job_id=job_id,
             sample_size=payload.sample_size,
             prompt_template=payload.prompt_template,
+            env_id=payload.env_id,
         )
         return result
     except ValueError as e: