Open files through TUI-WM: context-menu Open, double-click, editor fallback

- Double-clicking a file or choosing the new 'Öppna' context-menu item
  asks TUI-WM to open it via $TUI_WM_SOCKET (open_file), inheriting
  the user's file associations and default editor
- Outside TUI-WM the configured text_editor is used instead: the TUI
  suspends, runs the editor on the same terminal and resumes
- Directories keep navigating as before

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/main.rs

@@ -2,6 +2,7 @@ mod app;
 mod config;
 mod file_ops;
 mod theme;
+mod tui_wm;
 mod ui;
 mod events;