feat: VS-style dock tabs with middle-elision and full context menu

- Remove stylesheet from dock tab bars; handle all painting in
  MenuBarStyle (CE_TabBarTabShape + CE_TabBarTabLabel) so middle-
  elision actually works (QStyleSheetStyle was intercepting labels)
- Accent line on selected tab, dark background, bottom border
- Tab font synced with editor font for correct sizing
- Full right-click context menu: Close, Close All Tabs, Close All
  But This, Close All But Pinned, Copy Full Path, Open Containing
  Folder, Float/Dock, Pin/Unpin Tab, New Horizontal/Vertical
  Document Group
- Add View → Reset Windows to re-tabify all docks
- Remove old View → Split/Remove Split
- Guard deferred timer lambdas with QPointer<QDockWidget>
- Extract setupDockTabBars() for idempotent tab bar configuration
- Register close-all.svg and split-vertical.svg icons

src/resources.qrc

@@ -60,5 +60,9 @@
         <file alias="search.svg">vsicons/search.svg</file>
         <file alias="regex.svg">vsicons/regex.svg</file>
         <file alias="refresh.svg">vsicons/refresh.svg</file>
+        <file alias="pin.svg">vsicons/pin.svg</file>
+        <file alias="pinned.svg">vsicons/pinned.svg</file>
+        <file alias="close-all.svg">vsicons/close-all.svg</file>
+        <file alias="split-vertical.svg">vsicons/split-vertical.svg</file>
     </qresource>
 </RCC>