Make closures.osm.ch Production Ready

closures.osm.ch is a community-driven platform for reporting temporary road closures in real-time, built during GSoC 2025. It is not yet production-ready: the Valhalla routing integration is architecturally backwards (the frontend pushes coordinates to Valhalla rather than Valhalla pulling closure data), government data feeds are unsupported, and several features needed for real-world adoption remain incomplete. This project closes that gap across three pillars: (1) replacing the prototype routing integration with a correct architecture — a closure_sync sidecar service that feeds Valhalla's native live traffic tiles infrastructure, with a backend-served exclude_polygons endpoint as an immediate stepping-stone; (2) implementing CIFS and DATEX II importers to ingest authoritative government road closure data with attribution and deduplication; and (3) completing the remaining loose ends — a Mapbox Vector Tile overlay of active closures with Redis caching, and UI internationalisation via Transifex. Deliverables: self-hosted Valhalla instance, POST /api/v1/routing/closure-aware endpoint, frontend cleanup, CIFS and DATEX II importers with shared base class, GET /api/v1/tiles/{z}/{x}/{y}.mvt endpoint, and i18n wiring with English and German initial translations.