fix(sni): delay tray item insertion until proxies are ready

Only add tray widgets after the SNI proxy has finished initializing and the
item has a valid id/category pair.

This also removes invalid items through the host teardown path, refreshes the
tray when item status changes, and avoids calling DBus methods through a null
proxy during early clicks or scroll events.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

include/modules/sni/tray.hpp

@@ -19,6 +19,7 @@ class Tray : public AModule {
  private:
   void onAdd(std::unique_ptr<Item>& item);
   void onRemove(std::unique_ptr<Item>& item);
+  void queueUpdate();
 
   static inline std::size_t nb_hosts_ = 0;
   bool show_passive_ = false;