Improve preferences search UX, navigation, and add footer

- Enhanced search result selection to scroll exactly to the clicked
  item using `QTimer::singleShot` and `mapTo` for robust positioning.
- Added a 50ms debounce timer for search to improve responsiveness.
- Factored out `getSearchableText` helper for consistent search matching.
- Added a footer to the preferences list in `configdialog.ui` with
  text "The road goes no further." and a centered "Back to top" button.
- Refactored `ConfigDialog` to use `QSignalBlocker` for robust sidebar
  synchronization and removed the manual `m_suppressScrollSync` flag.
- Improved `slot_onScroll` to ensure the last section is selected in
  the sidebar when reaching the bottom.
- Updated `slot_cancel` to call `reject()` and improved metatype safety
  for widget pointers in search results using `QObject*`.
- Applied clang-format.

Author: nschimme

src/preferences/configdialog.cpp

@@ -123,7 +123,7 @@ ConfigDialog::ConfigDialog(QWidget *const parent)
 
     m_searchTimer = new QTimer(this);
     m_searchTimer->setSingleShot(true);
-    m_searchTimer->setInterval(250);
+    m_searchTimer->setInterval(50);
     connect(m_searchTimer, &QTimer::timeout, this, [this]() { slot_search(ui->searchBar->text()); });
     connect(ui->searchBar, &QLineEdit::textChanged, m_searchTimer, qOverload<>(&QTimer::start));
 

src/preferences/configdialog.ui

@@ -113,7 +113,7 @@
               </property>
              </widget>
             </item>
-            <item>
+            <item alignment="Qt::AlignmentFlag::AlignCenter">
              <widget class="QPushButton" name="backToTopBtn">
               <property name="sizePolicy">
                <sizepolicy hsizetype="Fixed" vsizetype="Fixed">
@@ -124,9 +124,6 @@
               <property name="text">
                <string>Back to top</string>
               </property>
-              <property name="flat">
-               <bool>true</bool>
-              </property>
              </widget>
             </item>
            </layout>