fix: standardize panel heading styles and prevent clipping (#198, #199)

- QDockWidget::title: add font-weight bold and text-align left to
  match ActionGroup header style
- ActionLabel header: add min-width 0 to prevent title clipping
  in narrow panels

Applied to both src/Gui/Stylesheets and resources/preferences copies.

resources/preferences/KindredCreate/KindredCreate.qss

@@ -247,6 +247,8 @@ QDockWidget {
 QDockWidget::title {
     background-color: #181825;
     color: #cdd6f4;
+    font-weight: bold;
+    text-align: left;
     padding: 8px 6px;
     border-bottom: 1px solid #313244;
     min-height: 18px;
@@ -1129,6 +1131,11 @@ QSint--ActionGroup QFrame {
     border-radius: 4px;
 }
 
+QSint--ActionGroup QSint--ActionLabel[class="header"] {
+    color: #cdd6f4;
+    min-width: 0;
+}
+
 /* Input Field */
 Gui--InputField {
     background-color: #313244;