Fix Edit/Delete on notes saved before properties.id existed

The earliest notes (saved before the previous commit added id
tracking) have no properties.id — update/delete target a feature by
that id, so offering Edit/Delete for one without it just 404s
("Could not delete/save the note", the generic fetch-failure alert).

The popup no longer offers Edit/Delete without an id. New
rake gpx:backfill_note_ids assigns one to any pre-existing Note
feature missing it, so already-saved notes become editable again too
— run once against wherever data/gpx actually lives (e.g. inside the
deployed container).

public/js/gpx.js

@@ -696,7 +696,10 @@ export class GpxPanelControl {
     this._map.on("click", layerId, (event) => {
       const feature = event.features[0];
       if (!feature) return;
-      const editable = feature.properties.category === "Note" && isLoggedIn();
+      // properties.id is what update/delete target by — a note saved before
+      // that existed (see `rake gpx:backfill_note_ids`) doesn't have one
+      // yet, and offering Edit/Delete for it would just 404.
+      const editable = feature.properties.category === "Note" && !!feature.properties.id && isLoggedIn();
       const popup = new Popup({ closeButton: true, maxWidth: "260px" })
         .setLngLat(event.lngLat)
         .setHTML(popupHtml(feature.properties, { editable }))