Add map previews to journal route and activity pages

- Route/activity list pages: map thumbnails with route drawn on OSM tiles
- Route/activity detail pages: interactive Leaflet map with zoom controls
- Server: expose GeoJSON from PostGIS via ST_AsGeoJSON (simplified for lists)
- RouteMapThumbnail component: shared, supports thumbnail and interactive modes
- Placeholder shown for routes/activities without geometry
- Archive journal-route-previews change, sync specs

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

apps/journal/app/components/RouteMapThumbnail.tsx

@@ -0,0 +1,51 @@
+import { useEffect, useRef } from "react";
+import { MapContainer, TileLayer, GeoJSON, useMap } from "react-leaflet";
+import L from "leaflet";
+import type { GeoJsonObject } from "geojson";
+import "leaflet/dist/leaflet.css";
+
+function FitBounds({ data }: { data: GeoJsonObject }) {
+  const map = useMap();
+  const fitted = useRef(false);
+  useEffect(() => {
+    if (fitted.current) return;
+    const layer = L.geoJSON(data);
+    const bounds = layer.getBounds();
+    if (bounds.isValid()) {
+      map.fitBounds(bounds, { padding: [20, 20] });
+      fitted.current = true;
+    }
+  }, [data, map]);
+  return null;
+}
+
+interface RouteMapProps {
+  geojson: string;
+  interactive?: boolean;
+  className?: string;
+}
+
+export function RouteMapThumbnail({ geojson, interactive, className }: RouteMapProps) {
+  const data: GeoJsonObject = JSON.parse(geojson);
+
+  return (
+    <MapContainer
+      center={[50, 10]}
+      zoom={6}
+      className={className ?? "h-36 w-full rounded"}
+      zoomControl={interactive ?? false}
+      attributionControl={interactive ?? false}
+      dragging={interactive ?? false}
+      scrollWheelZoom={interactive ?? false}
+      doubleClickZoom={interactive ?? false}
+      touchZoom={interactive ?? false}
+    >
+      <TileLayer
+        url="https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png"
+        attribution={interactive ? '&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a>' : undefined}
+      />
+      <GeoJSON data={data} style={{ color: "#2563eb", weight: 3, opacity: 0.8 }} />
+      <FitBounds data={data} />
+    </MapContainer>
+  );
+}