Add C++ code generator, rendered view, fix Hex node display

- Add generator.h/cpp: C++ struct emission with padding gaps, tail
  padding, pragma pack, static_assert, nested structs, pointers
- Add rendered view (QStackedWidget per tab, QsciScintilla + C++ lexer)
- View menu: C/C++ switches to rendered view, Reclass View switches back
- File > Export C++ Header writes full SDK to .h file
- Fix Hex8-Hex64 display: show name + value columns like normal types
  instead of hiding name behind ASCII preview (only Padding keeps that)
- Update column span detection, compose width calc, controller edit
  dispatch, and editor dimming to match new Hex layout
- Sample data: Entity struct with health, armor, speed, flags fields
- Add test_generator (21 tests) and test_validation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/resources.qrc

@@ -27,5 +27,9 @@
         <file alias="files.svg">vsicons/files.svg</file>
         <file alias="extensions.svg">vsicons/extensions.svg</file>
         <file alias="question.svg">vsicons/question.svg</file>
+        <file alias="eye.svg">vsicons/eye.svg</file>
+        <file alias="code.svg">vsicons/code.svg</file>
+        <file alias="export.svg">vsicons/export.svg</file>
+        <file alias="preview.svg">vsicons/preview.svg</file>
     </qresource>
 </RCC>