fix: curate swap endpoint name, reorder date field, 404 on missing asset

- Rename /curate/retag to /curate/swap; response now includes new_tag
- /curate/reorder: read body["order"] key (was ordered_ids); include date field
- /curate/remove and /curate/swap: return 404 if asset_id not found
- Update phase3.html JS fetch calls and reorder payload to match spec

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

services/travel-memories/app/templates/phase3.html

@@ -56,7 +56,7 @@ async function removeFn(albumId, assetId, el) {
 }
 
 async function retag(albumId, assetId, el) {
-  await fetch('/curate/retag', {
+  await fetch('/curate/swap', {
     method: 'POST',
     headers: {'Content-Type': 'application/json'},
     body: JSON.stringify({album_id: albumId, asset_id: assetId})
@@ -69,10 +69,11 @@ async function reorder(albumId, container) {
   var ids = Array.from(container.querySelectorAll('.photo-card')).map(function(e) {
     return e.dataset.assetId;
   });
+  var day = container.id.replace('day-', '');
   await fetch('/curate/reorder', {
     method: 'POST',
     headers: {'Content-Type': 'application/json'},
-    body: JSON.stringify({album_id: albumId, ordered_ids: ids})
+    body: JSON.stringify({album_id: albumId, date: day, order: ids})
   });
 }