Route desktop codec diagnostics through the shared log

Quiet capability probes, preserve runtime errors, and register the desktop portal application. Add logging and desktop launcher regression coverage.

tools/chatgui/src/gui_log.cpp

@@ -0,0 +1,17 @@
+#include "gui_log.h"
+#include "debug_config.h"
+#include <QByteArray>
+#include <QString>
+#include <cstring>
+
+static void guiLog(QtMsgType type, const QMessageLogContext& context, const QString& message) {
+    const debug_level_t level = type == QtDebugMsg ? DEBUG_LEVEL_DEBUG : type == QtInfoMsg ? DEBUG_LEVEL_INFO
+        : type == QtWarningMsg ? DEBUG_LEVEL_WARN : DEBUG_LEVEL_ERROR;
+    const char* name = context.category ? context.category : "default";
+    const int category = !strncmp(name, "qt.multimedia", 13) ? DEBUG_CATEGORY_VIDEO : DEBUG_CATEGORY_GENERAL;
+    if (!debug_should_output(level, category)) return;
+    const auto text = message.toUtf8();
+    debug_output(level, category, context.function, context.file, context.line, "Qt[%s]: %s", name, text.constData());
+}
+
+QtMessageHandler installGuiLogHandler() { return qInstallMessageHandler(guiLog); }