fix: seed discovery ring from server on initial page load

The ring was only populated from localStorage or during SPA navigation.
First visits (empty localStorage) or cross-shop visits (stale ring)
left ringProductIds empty, causing the related content sidebar to show
only the current product. Now:

- On page load, if localStorage ring is empty, fetch from watch JSON
- Invalidate stale rings when current product is not in the saved ring

make_post_sell/static/js/watch.js

@@ -217,6 +217,16 @@
         var initialId = initialProductEl.getAttribute('data-watch-product-id');
         currentProductId = initialId;
         markWatched(initialId);
+
+        // Invalidate stale ring (wrong shop or product removed from ring)
+        if (ringProductIds.length && ringProductIds.indexOf(initialId) === -1) {
+            ringProductIds = [];
+            ringPosition = 0;
+            ringHistory = {};
+            ringLoops = 0;
+            saveRingState();
+        }
+
         syncRingPosition(initialId);
         if (initialProductEl.getAttribute('data-watch-is-mod') === '1') {
             isMod = true;
@@ -1827,5 +1837,21 @@
     rebindToggles();
 
     renderQueue();
-    preloadNext();
+
+    // Seed ring from server if localStorage is empty (first visit, cache cleared)
+    if (!ringProductIds.length && currentProductId) {
+        fetchWatchData(currentProductId).then(function(data) {
+            if (data.ring && data.ring.length) {
+                ringProductIds = data.ring;
+                syncRingPosition(currentProductId);
+                saveRingState();
+                updateProgressDisplay();
+            }
+            preloadNext();
+        }).catch(function() {
+            preloadNext();
+        });
+    } else {
+        preloadNext();
+    }
 })();