feat(client): add client_update_scale and layersurface_update_scale

- client_update_scale(): re-notifies clients when output scale changes
  using current_outputs max scale (avoids stale c->mon for floating windows)
- layersurface_update_scale(): same logic for layer shell surfaces (static)
- Initialize current_scale on initial commit for both surface types
- Uses 0.001f tolerance for float comparison to prevent redundant events
- Falls back to c->mon->wlr_output->scale if no current_outputs

include/client.h

@@ -130,6 +130,7 @@ void client_send_close(Client *c);
 void client_set_border_color(Client *c, const float color[static 4]);
 void client_set_fullscreen(Client *c, int fullscreen);
 void client_set_scale(struct wlr_surface *s, float scale);
+void client_update_scale(Client *c);
 uint32_t client_set_size(Client *c, uint32_t width, uint32_t height);
 void client_set_tiled(Client *c, uint32_t edges);
 void client_set_suspended(Client *c, int suspended);