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>

packages/i18n/src/locales/de.ts

@@ -123,6 +123,7 @@ export default {
       distance: "Strecke",
       elevationGain: "Höhenmeter",
       noRoutesYet: "Noch keine Routen. Erstelle deine erste Route!",
+      noMapPreview: "Keine Kartenvorschau",
       saveChanges: "Änderungen speichern",
     },
     activities: {

packages/i18n/src/locales/en.ts

@@ -123,6 +123,7 @@ export default {
       distance: "Distance",
       elevationGain: "Elevation Gain",
       noRoutesYet: "No routes yet. Create your first route!",
+      noMapPreview: "No map preview",
       saveChanges: "Save Changes",
     },
     activities: {