fix: global blue highlight, Ctrl+F find bar with prev/next/close buttons

- Change QPalette::Highlight from theme.selection to theme.hover globally
- RcxEditor find: use SCI_SEARCHINTARGET + INDIC_COMPOSITIONTHICK indicator
  (selection rendering is disabled, so findFirst was invisible)
- Re-apply find indicators after applyDocument() refresh cycle
- Add prev/next/close buttons to find bars in both Reclass and C/C++ modes
- Buttons styled with hover/pressed states matching tab styling

src/mainwindow.h

@@ -101,6 +101,7 @@ private:
         RcxEditor*     editor    = nullptr;
         QsciScintilla* rendered  = nullptr;
         QLineEdit*     findBar   = nullptr;
+        QWidget*       findContainer = nullptr;
         QWidget*       renderedContainer = nullptr;
         ViewMode       viewMode  = VM_Reclass;
         uint64_t       lastRenderedRootId = 0;