W52: Tests for editor MarkAll, Close, BlockSave, InsertFile

Add 4 unit tests covering the new W50 editor commands:

- mark_all_selects_entire_buffer: verify selection covers
  the full buffer (start=0, end=buffer.len())
- close_clean_buffer_reopens_empty: verify Close on an
  unmodified buffer resets to an empty buffer
- block_save_on_no_selection_shows_message: verify the
  "No selection" message when nothing is selected
- insert_file_opens_insert_file_prompt: verify the mode
  switches to InsertFile prompt

Tests: 1415 pass (was 1411), zero warnings.

local/recipes/tui/tlc/source/src/editor/mod.rs

@@ -3873,5 +3873,45 @@ mod tests {
         e.push_goto_history(20);
         assert_eq!(e.goto_history, vec![10, 20]);
     }
+
+    #[test]
+    fn mark_all_selects_entire_buffer() {
+        let mut e = make_empty();
+        e.insert_str("hello world");
+        // Dispatch MarkAll via the dispatcher.
+        let _ = e.dispatch_editor_cmd(crate::editor::menubar::EditorCmd::MarkAll);
+        let sel = e.cursor.selection();
+        assert!(sel.is_some());
+        let (start, end) = sel.unwrap();
+        assert_eq!(start, 0);
+        assert_eq!(end, e.buffer.len());
+    }
+
+    #[test]
+    fn close_clean_buffer_reopens_empty() {
+        let mut e = make_empty();
+        e.insert_str("hello");
+        e.modified = false;
+        let _ = e.dispatch_editor_cmd(crate::editor::menubar::EditorCmd::Close);
+        // Should have reopened as an empty buffer.
+        assert_eq!(e.buffer.len(), 0);
+        assert!(!e.modified);
+    }
+
+    #[test]
+    fn block_save_on_no_selection_shows_message() {
+        let mut e = make_empty();
+        e.insert_str("hello");
+        e.cursor.clear_selection();
+        let _ = e.dispatch_editor_cmd(crate::editor::menubar::EditorCmd::BlockSave);
+        assert_eq!(e.message, Some("No selection".to_string()));
+    }
+
+    #[test]
+    fn insert_file_opens_insert_file_prompt() {
+        let mut e = make_empty();
+        let _ = e.dispatch_editor_cmd(crate::editor::menubar::EditorCmd::InsertFile);
+        assert!(e.mode.is_prompt());
+    }
 }