Array element offset display, fold arrow UX, type picker popup, and provider cleanup

- Show relative hex offset on array element separators ([N] +0x...)
- Dim fold arrows and add hover highlight for better visibility
- Extend fold/chevron click areas for easier interaction
- Add type picker popup for array element type and pointer target editing
- Remove process_provider.h in favor of plugin-based provider system
- Expand compose/format to handle struct-of-array type names and widths

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

src/editor.h

@@ -65,6 +65,7 @@ signals:
                              EditTarget target, const QString& text);
     void inlineEditCancelled();
     void typeSelectorRequested();
+    void typePickerRequested(EditTarget target, int nodeIdx, QPoint globalPos);
 
 protected:
     bool eventFilter(QObject* obj, QEvent* event) override;