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/typeselectorpopup.h

@@ -25,11 +25,12 @@ public:
     explicit TypeSelectorPopup(QWidget* parent = nullptr);
 
     void setFont(const QFont& font);
+    void setTitle(const QString& title);
     void setTypes(const QVector<TypeEntry>& types, uint64_t currentId);
     void popup(const QPoint& globalPos);
 
 signals:
-    void typeSelected(uint64_t structId);
+    void typeSelected(uint64_t id, const QString& displayName);
     void createNewTypeRequested();
     void dismissed();