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/mcp/mcp_bridge.cpp

@@ -796,7 +796,8 @@ QJsonObject McpBridge::toolSourceSwitch(const QJsonObject& args) {
         uint32_t pid = (uint32_t)args.value("pid").toInteger();
         QString name = args.value("processName").toString();
         if (name.isEmpty()) name = QString("PID %1").arg(pid);
-        ctrl->attachToProcess(pid, name);
+        QString target = QString("%1:%2").arg(pid).arg(name);
+        ctrl->attachViaPlugin(QStringLiteral("processmemory"), target);
         return makeTextResult("Attached to process " + name + " (PID " + QString::number(pid) + ")");
     }