Add protocol:nostr to saved feed queries for latest results

The previous useStreamPosts always injected 'protocol:nostr' into the
NIP-50 search string, which is a Ditto relay extension that filters for
native Nostr events. Without it, useTabFeed's queries return stale or
fewer results because the relay doesn't scope to the Nostr protocol.

Augment the resolved filter's search field with 'protocol:nostr' before
passing it to useTabFeed, matching the old behavior.

src/components/Feed.tsx

@@ -374,13 +374,25 @@ function SavedFeedContent({ feed }: { feed: SavedFeed }) {
     user?.pubkey ?? '',
   );
 
+  // Augment the resolved filter with protocol:nostr (NIP-50 Ditto extension)
+  // to match the behavior of the core feeds and ensure latest native Nostr
+  // posts are returned.
+  const augmentedFilter = useMemo(() => {
+    if (!resolvedFilter) return null;
+    const existing = resolvedFilter.search ?? '';
+    const search = existing
+      ? `${existing} protocol:nostr`
+      : 'protocol:nostr';
+    return { ...resolvedFilter, search };
+  }, [resolvedFilter]);
+
   const {
     data: rawData,
     isLoading: isFeedLoading,
     fetchNextPage,
     hasNextPage,
     isFetchingNextPage,
-  } = useTabFeed(resolvedFilter, `saved-${feed.id}`, !isResolving);
+  } = useTabFeed(augmentedFilter, `saved-${feed.id}`, !isResolving);
 
   const isLoading = isResolving || isFeedLoading;