Work around startup UI freeze caused by QtTextToSpeech

This merge request works around an annoying startup hang that I introduced when adding text-to-speech to NeoChat. The previous implementation was a QML singleton that used the `TextToSpeech` QML component. Unfortunately that component blocks the UI thread when first loading it, while it connects to speech-dispatcher.

This MR just rewrites that singleton in C++, and moves initialization of QtTextToSpeech to the first time you read a message aloud. It doesn't fix the performance problem, but it at least stops it from affecting startup.

In the future, I'd like to move speech operations to a background thread to completely mitigate the initialization freeze.

src/app/qml/Main.qml

@@ -196,7 +196,6 @@ Kirigami.ApplicationWindow {
         NeoChatSettingsView.window = root;
         NeoChatSettingsView.connection = root.connection;
         WindowController.setBlur(pageStack, NeoChatConfig.blur && !NeoChatConfig.compactLayout);
-        TextToSpeechWrapper.warmUp();
         if (ShareHandler.text && root.connection) {
             root.handleShare()
         }

src/app/qml/TextToSpeechWrapper.qml

@@ -1,24 +0,0 @@
-// SPDX-FileCopyrightText: 2025 Ritchie Frodomar <alkalinethunder@gmail.com>
-// SPDX-License-Identifier: GPL-2.0-or-later
-
-pragma Singleton
-
-import QtQuick
-import QtTextToSpeech
-
-QtObject {
-    id: root
-
-    readonly property TextToSpeech tts: TextToSpeech {
-        id: tts
-    }
-
-    function warmUp() {
-        // TODO: This method is called on startup to avoid a UI freeze the first time you read a message aloud, but there's nothing for it to do.
-        // This would be a good place to check if TTS can actually be used.
-    }
-
-    function say(text: String) {
-        tts.say(text)
-    }
-}