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/core.h

@@ -650,7 +650,7 @@ inline ColumnSpan commandRowRootNameSpan(const QString& lineText) {
 inline ColumnSpan commandRowChevronSpan(const QString& lineText) {
     if (lineText.size() < 3) return {};
     if (lineText[0] == '[' && lineText[1] == QChar(0x25B8) && lineText[2] == ']')
-        return {0, 3, true};
+        return {0, qMin(4, (int)lineText.size()), true};  // include trailing space for easier clicking
     return {};
 }