fix: align OverlayViewModel message dedup with ChatViewModel

Removed the legacy isDup check (role+content+msgType) that could suppress
multi_message items already seen as review items. Now deduplicates by
message ID only and inserts at correct timestamp position, matching
the fixed ChatViewModel behavior.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/src/main/java/top/yeij/cyrene/viewmodel/OverlayViewModel.kt

@@ -80,20 +80,17 @@ class OverlayViewModel(
             chatRepository.observeMessages().collect { message ->
                 _messages.update { list ->
                     val updated = list.toMutableList()
-                    val idx = updated.indexOfLast { it.id == message.id }
-                    if (idx >= 0) {
-                        updated[idx] = message
+                    val existingIdx = updated.indexOfLast { it.id == message.id }
+                    if (existingIdx >= 0) {
+                        updated[existingIdx] = message
                     } else {
-                        val isDup = updated.any {
-                            it.role == message.role && it.content == message.content && it.msgType == message.msgType
-                        }
-                        if (!isDup) {
-                            updated.add(message)
+                        // Insert at correct position for ascending timestamp (oldest first for top-down layout)
+                        val insertAt = updated.indexOfFirst { it.timestamp >= message.timestamp }
+                        if (insertAt >= 0) updated.add(insertAt, message) else updated.add(message)
                         val animIdx = _messageAnimIndex.value.toMutableMap()
                         animIdx[message.id] = animCounter++
                         _messageAnimIndex.value = animIdx
                     }
-                    }
                     updated.deduplicate()
                 }