ui+ci: style KDDockWidgets tabs and add Applications symlink to DMG

- Add explicit QTabBar::tab styles to olive-dark/style.css so inactive
  KDDockWidgets tabs render with a dark background and white text instead
  of falling back to the native macOS light tab appearance.
- Update macOS CD to stage Oak.app alongside an Applications symlink
  before creating the DMG, matching standard macOS installer disk images.

.github/workflows/cd.yml

@@ -269,8 +269,11 @@ jobs:
 
       - name: Create DMG
         run: |
+          mkdir -p build/app/dmg-staging
+          cp -R build/app/Oak.app build/app/dmg-staging/
+          ln -s /Applications build/app/dmg-staging/Applications
           hdiutil create \
-            -srcfolder build/app/Oak.app \
+            -srcfolder build/app/dmg-staging \
             -volname "Oak Video Editor" \
             -fs HFS+ \
             -format UDZO \

app/ui/style/olive-dark/style.css

@@ -27,3 +27,30 @@ QPushButton:checked {
 QTabBar {
     font-size: 9pt;
 }
+
+/* Force KDDockWidgets / QTabBar tabs to use dark palette colors.
+   On macOS the native tab style can otherwise render light backgrounds
+   with light text, making inactive tabs unreadable. */
+QTabBar::tab {
+    background: #353535;
+    color: #FFFFFF;
+    border: 1px solid #2a2a2a;
+    padding: 4px 10px;
+}
+
+QTabBar::tab:selected {
+    background: #2A82DA;
+    color: #FFFFFF;
+}
+
+QTabBar::tab:hover {
+    background: #404040;
+}
+
+QTabBar::tab:!selected {
+    margin-top: 2px;
+}
+
+QTabBar::close-button {
+    image: none;
+}