Add tmux window movement keybindings and update documentation

- Add Ctrl-Shift-Left/Right keybindings to quickly move windows
- Update README with comprehensive tmux keybindings documentation
  - Organize keybindings into categories: Pane, Window, Session & Config
  - Document all existing and new keybindings
  - Add descriptions for better clarity

🤖 Generated with [Claude Code](https://claude.ai/code)

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

modules/tmux.nix

@@ -102,6 +102,10 @@
       
       # Automatically renumber windows
       set -g renumber-windows on
+      
+      # Quick window movement
+      bind-key -n C-S-Left swap-window -t -1\; select-window -t -1
+      bind-key -n C-S-Right swap-window -t +1\; select-window -t +1
     '';
   };
 }