feat: separate favorite relay feeds into their own category in nav popup

Relay feeds were previously grouped under the generic "Feeds" category
in the top nav bar filter dialog. This adds a dedicated "Relays" group
so users can more easily find their favorite relay feeds.

https://claude.ai/code/session_016gjbPgYRXrQCoY1zKPz5PX

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/topbars/FeedFilterSpinner.kt

@@ -328,6 +328,7 @@ private enum class FeedGroup(
     HASHTAGS(R.string.feed_group_hashtags),
     COMMUNITIES(R.string.feed_group_communities),
     LISTS(R.string.feed_group_lists),
+    RELAYS(R.string.feed_group_relays),
 }
 
 private fun groupFeedDefinitions(options: ImmutableList<FeedDefinition>): Map<FeedGroup, List<IndexedFeedDefinition>> {
@@ -337,6 +338,7 @@ private fun groupFeedDefinitions(options: ImmutableList<FeedDefinition>): Map<Fe
             is HashtagName -> FeedGroup.HASHTAGS
             is CommunityName -> FeedGroup.COMMUNITIES
             is PeopleListName -> FeedGroup.LISTS
+            is RelayName -> FeedGroup.RELAYS
             else -> FeedGroup.FEEDS
         }
     }

amethyst/src/main/res/values/strings.xml

@@ -1567,6 +1567,7 @@
     <string name="feed_group_hashtags">Hashtags</string>
     <string name="feed_group_communities">Communities</string>
     <string name="feed_group_lists">Lists</string>
+    <string name="feed_group_relays">Relays</string>
 
     <string name="temporary_account">Log off on device lock</string>
     <string name="private_message">Private Message</string>