feat: phase A — backup B2, healthcheck /api/status, vector tiles Tippecanoe

- A1: scripts/backup-postgres.sh — pg_dump quotidien compressé → Backblaze B2 (rclone), rétention 30j
- A2: StatusController retourne HTTP 503 + healthy/alertReason si dernière observation > 6h
- A4: Dockerfile installe tippecanoe, GenerateTilesCommand génère 5 tilesets (obs + h6/12/24/48), Caddyfile sert /tiles/* sans fallback SPA, SargassesMap.jsx passe en sources vector tiles statiques
- chore: backend/public/assets/ ajouté au .gitignore (build artifacts)
- chore: setup vitest frontend + ImpactScoreServiceTest (session précédente)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/vite.config.js

@@ -14,6 +14,11 @@ const cleanAssetsPlugin = () => ({
 
 export default defineConfig({
   plugins: [react(), cleanAssetsPlugin()],
+  test: {
+    environment: 'jsdom',
+    globals: true,
+    setupFiles: './src/test/setup.js',
+  },
   server: {
     proxy: {
       '/api': {