Add per-day map coloring and remaining unit tests

- RouteMapThumbnail: Color route segments per day with alternating colors
  when dayBreaks are present, pass through from route detail page
- overnight.test.ts: 6 tests for isOvernight/setOvernight with Y.Doc
- daybreaks-extraction.test.ts: 3 tests for GPX → dayBreaks index extraction

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/journal/app/routes/routes.$id.tsx

@@ -202,7 +202,7 @@ export default function RouteDetailPage({ loaderData }: Route.ComponentProps) {
 
       {route.geojson && (
         <div className="mt-6 overflow-hidden rounded-lg border border-gray-200" style={{ height: 400 }}>
-          <ClientMap geojson={route.geojson} interactive className="h-full w-full" />
+          <ClientMap geojson={route.geojson} interactive className="h-full w-full" dayBreaks={route.dayBreaks.length > 0 ? route.dayBreaks : undefined} />
         </div>
       )}