fix: dedupe Discover apps by coordinate to avoid duplicate LazyGrid keys

The Browser home "Discover nsites/napplets" sections render each followed
manifest in a LazyVerticalGrid keyed by "ns:"/"np:" + coordinate. The
observed store (NoteListMatchingFilter, backed by a ConcurrentSkipListSet
ordered by created-at/id) can surface the same addressable note twice when a
replaceable manifest gets a new version — mutating the note's sort key inside
the set breaks dedup. Both copies map to the same coordinate, producing a
duplicate grid key and crashing with IllegalArgumentException.

Collapse the mapped list by coordinate so each app appears once and grid keys
stay unique.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01P9TomvuP9YnPUDCZuiQae6

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/browser/BrowserScreen.kt

@@ -619,6 +619,10 @@ private fun List<Note>.toDiscoverApps(
             matchAuthor(author)
         }.mapNotNull { it.toDiscoverNostrApp() }
         .filter { it.app.coordinate !in excludeCoordinates }
+        // The observed store can surface the same addressable manifest twice (a replaceable note whose
+        // new version mutates its sort key inside the backing set), so collapse by coordinate to keep the
+        // grid keys unique — otherwise LazyVerticalGrid throws on the duplicate "ns:"/"np:" key.
+        .distinctBy { it.app.coordinate }
         .take(DISCOVER_NOSTR_LIMIT)
         .toList()