feat: add combined environment endpoint for concurrent weather + air quality fetch

- POST /volatile/fetch/environment/{city} fetches both in parallel
- Single geocode lookup shared between API calls
- Uses asyncio.gather() for concurrent external requests
- Fix scheduler executor name (rest_api → rest_api_executor)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "library-desk"
-version = "1.6.2"
+version = "1.7.0"
 description = "Coordination service for The Library system - HybridRAG queries, document ingestion, entity extraction, and knowledge consolidation"
 readme = "README.md"
 requires-python = ">=3.12"