feat: kernel memory plugin + unified source menu + driver improvements

- KernelMemory plugin: kernel-mode process/physical memory R/W via IOCTL driver
- rcxdrv.sys: MmCopyMemory for reads, MDL mapping with correct cache types
  (MmCached for RAM, MmNonCached for MMIO only — fixes cache corruption BSOD)
- Driver reconnect: ensureDriverLoaded tries device handle first, no auto
  stop+delete cycle. Manual unload closes handle only, service stays running.
- Unified source menu: ProviderRegistry::populateSourceMenu() shared by both
  main window Data Source menu and RcxEditor inline picker (icons + dll names)
- IProviderPlugin::populatePluginMenu() for conditional plugin actions
  (e.g. "Unload Kernel Driver" only when loaded)
- Physical memory mode removed from selectTarget (access via context menu only)
- requestOpenProviderTab sets base address from provider after template load
- Address parser: vtop(), cr3(), physRead() callbacks for kernel paging expressions

src/providerregistry.h

@@ -7,6 +7,13 @@
 // Forward declarations
 namespace rcx { class Provider; }
 class QWidget;
+class QMenu;
+
+// Lightweight struct for saved source display in menus
+struct SavedSourceDisplay {
+    QString text;
+    bool active = false;
+};
 
 /**
  * Global registry for data source providers
@@ -56,7 +63,13 @@ public:
     
     // Clear all providers
     void clear();
-    
+
+    // Populate a QMenu with source items (File, providers with icons/dll names,
+    // plugin actions, saved sources). Used by both the main window Data Source
+    // menu and the RcxEditor inline source picker.
+    static void populateSourceMenu(QMenu* menu,
+                                   const QVector<SavedSourceDisplay>& savedSources = {});
+
 private:
     ProviderRegistry() = default;
     QList<ProviderInfo> m_providers;