chatgui: channel sorting by name or last message time with preview

- Add last_msg_at column to channels table
- Update last_msg_at on every message insert (send/receive)
- Parameterize getChannels() with ChannelSortMode enum (Alphabetical/Recent)
- Add getChannelLastMessage() for preview text in channel list
- Add sorting combo to Profile settings page (stored in ui_state)
- Reload channels on message receive when sort is recent

tools/chatgui/db/db_manager.cpp

@@ -105,13 +105,17 @@ QByteArray DbManager::colBlob(sqlite3_stmt* stmt, int col) {
 
 /* ── channels ── */
 
-QList<ChannelRow> DbManager::getChannels() const {
+QList<ChannelRow> DbManager::getChannels(ChannelSortMode sort) const {
     QList<ChannelRow> list;
-    sqlite3_stmt* stmt = prepareOrNull(
+    const char* orderBy = (sort == ChannelSortMode::Recent)
+        ? " ORDER BY last_msg_at DESC, name COLLATE NOCASE ASC"
+        : " ORDER BY name COLLATE NOCASE ASC";
+    char sql[512]; snprintf(sql, sizeof(sql),
         "SELECT channel_id, name, owner_node_id,"
         " x25519_pubkey, x25519_privkey, ed25519_pubkey, ed25519_privkey, signature,"
-        " last_read_msg_id, last_pos_msg_id, created_at"
-        " FROM channels ORDER BY created_at ASC");
+        " last_read_msg_id, last_pos_msg_id, last_msg_at, created_at"
+        " FROM channels%s", orderBy);
+    sqlite3_stmt* stmt = prepareOrNull(sql);
     if (!stmt) return list;
     while (sqlite3_step(stmt) == SQLITE_ROW) {
         ChannelRow r;
@@ -125,7 +129,8 @@ QList<ChannelRow> DbManager::getChannels() const {
         r.signature       = colBlob(stmt, 7);
         r.lastReadMsgId   = sqlite3_column_int64(stmt, 8);
         r.lastPosMsgId    = sqlite3_column_int64(stmt, 9);
-        r.createdAt       = sqlite3_column_int64(stmt, 10);
+        r.lastMsgAt       = sqlite3_column_int64(stmt, 10);
+        r.createdAt       = sqlite3_column_int64(stmt, 11);
         list.append(r);
     }
     sqlite3_finalize(stmt);
@@ -139,6 +144,27 @@ QList<ChannelRow> DbManager::getChannels() const {
     return list;
 }
 
+QString DbManager::getChannelLastMessage(const QString& channelId) const {
+    QString sql = QStringLiteral(
+        "SELECT node_id, data FROM \"%1\" ORDER BY id DESC LIMIT 1")
+        .arg(msgTableName(channelId));
+    sqlite3_stmt* stmt = prepareOrNull(sql.toUtf8().constData());
+    if (!stmt) return {};
+    QString result;
+    if (sqlite3_step(stmt) == SQLITE_ROW) {
+        quint64 author = (quint64)sqlite3_column_int64(stmt, 0);
+        QByteArray jdata = colBlob(stmt, 1);
+        QString text = QString::fromUtf8(parseJsonField(jdata, "d"));
+        if (text.isEmpty()) text = QString::fromUtf8(parseJsonField(jdata, "ct"));
+        QString nick = getDisplayName(author);
+        QString shortText = text.left(60);
+        if (text.size() > 60) shortText += QStringLiteral("...");
+        result = nick + QStringLiteral(": ") + shortText;
+    }
+    sqlite3_finalize(stmt);
+    return result;
+}
+
 /* ── messages (UI) ── */
 
 QList<MessageRow> DbManager::getMessages(const QString& chId, int limit) const {