gui: fix Qt5/KF5 compatibility

- Remove placeholderText from QML palette block (not available in Qt5)
- Use theme.placeholderTextColor directly instead of palette.placeholderText
- Add Qt version guards for QFontDatabase static vs instance API
- Add Qt version guard for QVariant::typeId vs QVariant::type
- Link KF5::ConfigCore for ollie-gui KF5 build

CMakeLists.txt

@@ -108,6 +108,7 @@ if(OLLIE_KF5)
         Qt5::Quick
         Qt5::Qml
         Qt5::QuickControls2
+        KF5::ConfigCore
     )
 
     # --- Install ---

gui/main-kf5.qml

@@ -29,7 +29,6 @@ ApplicationWindow {
         dark: theme.darkColor
         light: theme.lightColor
         shadow: theme.shadowColor
-        placeholderText: theme.placeholderTextColor
     }
 
     // --- Settings Dialog ---
@@ -371,7 +370,7 @@ ApplicationWindow {
                             ? "(waiting for output...)"
                             : "Select or create a session")
                         font.family: "monospace"
-                        color: dbus.chatText ? palette.text : palette.placeholderText
+                        color: dbus.chatText ? palette.text : theme.placeholderTextColor
                         background: null
 
                         onTextChanged: {

gui/main.cpp

@@ -19,7 +19,11 @@ static QIcon makeBrainIcon()
 
     // Fallback: render FA6 brain glyph from installed font
     QFont fa("Font Awesome 6 Free Solid");
+#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
     if (!QFontDatabase::hasFamily("Font Awesome 6 Free Solid")) {
+#else
+    if (!QFontDatabase().families().contains("Font Awesome 6 Free Solid")) {
+#endif
         fa = QFont("Font Awesome 6 Free");
         fa.setWeight(QFont::Black);
     }

gui/thememanager.cpp

@@ -242,7 +242,11 @@ QPalette ThemeManager::paletteFromScheme(const QString &path) const
 QColor ThemeManager::parseColor(const QVariant &value) const
 {
     QStringList parts;
+#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
     if (value.typeId() == QMetaType::QStringList) {
+#else
+    if (value.type() == QVariant::StringList) {
+#endif
         parts = value.toStringList();
     } else {
         parts = value.toString().split(',');
@@ -329,7 +333,11 @@ void ThemeManager::setFontStyle(const QString &style)
 
 QStringList ThemeManager::availableFamilies() const
 {
+#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
     return QFontDatabase::families();
+#else
+    return QFontDatabase().families();
+#endif
 }
 
 QStringList ThemeManager::availableStyles() const
@@ -337,7 +345,11 @@ QStringList ThemeManager::availableStyles() const
     QString family = m_fontFamily.isEmpty()
         ? QGuiApplication::font().family()
         : m_fontFamily;
+#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
     return QFontDatabase::styles(family);
+#else
+    return QFontDatabase().styles(family);
+#endif
 }
 
 void ThemeManager::resetFont()
@@ -372,8 +384,13 @@ void ThemeManager::applyFont()
     if (!m_fontStyle.isEmpty()) {
         // Use QFontDatabase to resolve style string to weight + italic
         QString family = m_fontFamily.isEmpty() ? font.family() : m_fontFamily;
+#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
         QFont styled = QFontDatabase::font(family, m_fontStyle,
                                            m_fontSize > 0 ? m_fontSize : font.pointSize());
+#else
+        QFont styled = QFontDatabase().font(family, m_fontStyle,
+                                            m_fontSize > 0 ? m_fontSize : font.pointSize());
+#endif
         font.setWeight(styled.weight());
         font.setItalic(styled.italic());
     }