Fix patch browser keyboard navigation to cover directory rows

Arrow keys now navigate the full virtual row list (../, subdirs, patches)
rather than only patch rows. Landing on a patch auto-loads it as before;
landing on .. or a subdir highlights it and Enter confirms navigation.
Added patchVCursor to UIState to track keyboard focus independently of
the loaded patch. Mouse-click on a patch now also syncs the cursor so
subsequent arrow-key movement starts from the right position.

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

include/ui.h

@@ -72,6 +72,7 @@ typedef struct {
     char patchCurrentDir[256];
     char patchSubDirs[PATCH_MAX_DIRS][PATCH_NAME_LEN];
     int  patchSubDirCount;
+    int  patchVCursor;
 
     // Control registry — built lazily by uiKnob/uiSlider for CC mapping persistence
     UIControlEntry controlRegistry[128];