Method buildUI

src/gui/MainWindow.cpp:3765–4712

// buildMenuBar() lives in MainWindow_Menus.cpp (#3351 Phase 1b).

void MainWindow::buildUI()
{
    // ── Title bar + central splitter ─────────────────────────────────────────
    m_titleBar = new TitleBar(this);
    // Embed the menu bar into the title bar (left side)
    m_titleBar->setMenuBar(menuBar());
    updatePcAudioTooltip();
    connect(m_audio, &AudioEngine::inputDeviceChanged,
            this, &MainWindow::updatePcAudioTooltip, Qt::QueuedConnection);
    connect(m_audio, &AudioEngine::outputDeviceChanged,
            this, &MainWindow::updatePcAudioTooltip, Qt::QueuedConnection);
    connect(m_titleBar, &TitleBar::multiFlexClicked,
            this, &MainWindow::showMultiFlexDialog);
    connect(m_titleBar, &TitleBar::minimalModeRequested, this, [this]() {
        toggleMinimalMode(!m_minimalMode);
        if (m_minimalModeAction) {
            QSignalBlocker b(m_minimalModeAction);
            m_minimalModeAction->setChecked(m_minimalMode);
        }
    });
    connect(m_titleBar, &TitleBar::minimalModeWindowedExitRequested, this, [this]() {
        toggleMinimalMode(false);
    });
    // Title-bar dock-side click: clicking the active-side icon hides the
    // applet panel; clicking the inactive-side icon moves it there (and
    // shows it if hidden).
    auto handleDockClick = [this](bool wantLeft) {
        // If currently floating, dock back first so the float window is
        // torn down via the canonical path; otherwise reparenting the
        // contents into the splitter leaves an empty float window alive
        // and visible (the "black box" in #2584).
        if (m_appletPanelFloatWindow) {
            toggleAppletPanelFloating(false);
        }
        const bool dockedLeft = AppSettings::instance()
            .value("AppletPanelDockedLeft", "False").toString() == "True";
        const bool visible = m_appletPanel && m_appletPanel->isVisible();
        if (visible && dockedLeft == wantLeft) {
            setAppletPanelVisible(false);
        } else {
            if (!visible) setAppletPanelVisible(true);
            if (dockedLeft != wantLeft) setAppletPanelDockedLeft(wantLeft);
        }
    };
    connect(m_titleBar, &TitleBar::dockAppletLeftRequested,  this, [handleDockClick]() { handleDockClick(true);  });
    connect(m_titleBar, &TitleBar::dockAppletRightRequested, this, [handleDockClick]() { handleDockClick(false); });
    // Pop-out icon: toggle floating via the shared helper so the icon, the
    // Ctrl+Shift+S shortcut, and the float-window close-X stay in sync.
    connect(m_titleBar, &TitleBar::popOutAppletRequested, this, [this]() {
        toggleAppletPanelFloating(m_appletPanelFloatWindow == nullptr);
    });

    m_splitter = new QSplitter(Qt::Horizontal, this);
    m_splitter->setHandleWidth(0);

    auto* central = new QWidget(this);
    auto* vbox = new QVBoxLayout(central);
    vbox->setContentsMargins(0, 0, 0, 0);