fix(virtual_list): Move footer display buffer to state struct

- Added footer_display_buf and footer_display_len to VirtualListState
- Fixes use-after-return bug: stack buffer passed to pushCommand() was
  invalidated when function returned, causing corrupted display in
  deferred rendering

src/widgets/virtual_list/state.zig

@@ -112,6 +112,14 @@ pub const VirtualListState = struct {
     /// Frame counter para animaciones
     frame_count: u32 = 0,
 
+    // =========================================================================
+    // Buffers persistentes para texto formateado (evitar stack buffer escape)
+    // =========================================================================
+    // IMPORTANTE: Los buffers de stack pasados a ctx.pushCommand() se invalidan
+    // cuando la función retorna. El render diferido usaría memoria corrupta.
+    footer_display_buf: [96]u8 = undefined,
+    footer_display_len: usize = 0,
+
     const Self = @This();
 
     // =========================================================================

src/widgets/virtual_list/virtual_list.zig

@@ -710,7 +710,7 @@ fn drawFooter(
         colors.header_background,
     ));
 
-    // Format count
+    // Format count (usar buffers temporales solo para strings intermedios)
     var count_buf: [64]u8 = undefined;
     const count_info = list_state.getDisplayCount();
     const count_str = count_info.format(&count_buf);
@@ -725,14 +725,16 @@ fn drawFooter(
     else
         "-";
 
-    // Combine: "pos de total"
+    // Combine: "pos de total" - USAR BUFFER PERSISTENTE del state
-    var display_buf: [96]u8 = undefined;
+    // IMPORTANTE: Los buffers de stack se invalidan al retornar. El render
-    const display_str = std.fmt.bufPrint(&display_buf, "{s} de {s}", .{ pos_str, count_str }) catch "...";
+    // diferido necesita buffers que sobrevivan hasta después del execute().
+    const display_str = std.fmt.bufPrint(&list_state.footer_display_buf, "{s} de {s}", .{ pos_str, count_str }) catch "...";
+    list_state.footer_display_len = display_str.len;
 
     ctx.pushCommand(Command.text(
         bounds.x + 4,
         bounds.y + 2,
-        display_str,
+        list_state.footer_display_buf[0..list_state.footer_display_len],
         colors.text,
     ));
 }