chatgui: remember last read message, restore scroll position, show unread count badge

Store read/scroll positions per channel via ui_state table (key-value).
Draw red +N badge on channel list items for unread messages.
Fix getMessages() to fetch last N messages (was fetching first N).

tools/chatgui/db/db_manager.cpp

@@ -116,6 +116,9 @@ QList<ChannelRow> DbManager::getChannels() const {
         list.append(r);
     }
     sqlite3_finalize(stmt);
+    for (auto& ch : list) {
+        ch.unreadCount = getUnreadCount(ch.channelId, ch.lastReadMsgId);
+    }
     return list;
 }
 
@@ -125,7 +128,7 @@ QList<MessageRow> DbManager::getMessages(const QString& chId, int limit) const {
     QList<MessageRow> list;
     QString sql = QStringLiteral(
         "SELECT id, node_id, data, timestamp, chain_hash, author_signature"
-        " FROM \"%1\" ORDER BY timestamp, author_signature ASC LIMIT ?").arg(msgTableName(chId));
+        " FROM \"%1\" ORDER BY timestamp DESC, author_signature DESC LIMIT ?").arg(msgTableName(chId));
     sqlite3_stmt* stmt = prepareOrNull(sql.toUtf8().constData());
     if (!stmt) return list;
     sqlite3_bind_int(stmt, 1, limit);
@@ -157,7 +160,7 @@ QList<MessageRow> DbManager::getMessages(const QString& chId, int limit) const {
         m.signature    = colBlob(stmt, 5);
         m.isOutgoing   = (m.authorNodeId == myId);
         m.isRead       = true;
-        list.append(m);
+        list.prepend(m);
     }
     sqlite3_finalize(stmt);
     return list;
@@ -383,6 +386,26 @@ int DbManager::getUiStateInt(const QString& key, int defaultVal) const {
     return ok ? v : defaultVal;
 }
 
+qint64 DbManager::getUiStateInt64(const QString& key, qint64 defaultVal) const {
+    QString val = getUiState(key);
+    if (val.isEmpty()) return defaultVal;
+    bool ok = false;
+    qint64 v = val.toLongLong(&ok);
+    return ok ? v : defaultVal;
+}
+
+int DbManager::getUnreadCount(const QString& channelId, qint64 lastReadMsgId) const {
+    QString sql = QStringLiteral(
+        "SELECT COUNT(*) FROM \"%1\" WHERE id > ?").arg(msgTableName(channelId));
+    sqlite3_stmt* stmt = prepareOrNull(sql.toUtf8().constData());
+    if (!stmt) return 0;
+    sqlite3_bind_int64(stmt, 1, lastReadMsgId);
+    int count = 0;
+    if (sqlite3_step(stmt) == SQLITE_ROW) count = sqlite3_column_int(stmt, 0);
+    sqlite3_finalize(stmt);
+    return count;
+}
+
 /* ── sync operations (read-only, for gui_bridge) ── */
 
 QByteArray DbManager::syncListChannels() const {