Begin, the Lag Wars Have (#21839)

<img width="700" height="848" alt="image"
src="https://github.com/user-attachments/assets/e0db50af-35db-43c7-b78e-6c1ea5ac569c"
/>

you take a tiny little two year LOA and this happens
this PR hits some large lag culprits:
- UpdateOverlays() getting spammed by human/update_icon. This was 0.85%
of server CPU time during the event. Doesn't sound like a whole lot but
it's insane. 99% of it was caused by sloppy duplicate calls of
update_icon in set_dir (as well as update icon itself!). Refactored to
stop that
- Makes Follow menu update manually, which cuts down on the 2.8 million
REF() calls it made during the event. This was ~1% of CPU time including
ui_data as well.
- Gets rid of a bunch of random runtimes and some lighting-related
harddels.
- NanoUIs now clean themselves up when their owner qdels rather than
forcing the owner to do REF(src) and close all matching UIs. saves us
~0.1% server cpu time! wowza!

code/modules/nano/modules/follow_menu.dm

@@ -1,3 +1,5 @@
+GLOBAL_DATUM_INIT(follow_menu, /datum/tgui_module/follow_menu, new)
+
 /datum/tgui_module/follow_menu/ui_interact(var/mob/user, var/datum/tgui/ui)
 	ui = SStgui.try_update_ui(user, src, ui)
 	if(!ui)
@@ -14,9 +16,15 @@
 		return
 
 	if(action == "follow_target")
-		ghost.ManualFollow(locate(params["follow_target"]) in GLOB.mob_list)
+		if(!ghost.ManualFollow(locate(params["follow_target"]) in GLOB.mob_list))
+			to_chat(ghost, SPAN_WARNING("Failed to follow selected target. Refreshing mob list..."))
+			return TRUE
 
-/datum/tgui_module/follow_menu/ui_data(mob/user)
+	if(action == "refresh")
+		ui.send_full_update()
+		return TRUE
+
+/datum/tgui_module/follow_menu/ui_static_data(mob/user)
 	var/list/data = list()
 	// Don't worry about this is_mod check being for storytellers as well - all it does is highlight antags in red.
 	var/is_mod = check_rights(R_MOD|R_ADMIN, 0, user) || isstoryteller(user)

code/modules/nano/nanoui.dm

@@ -519,7 +519,7 @@ nanoui is used to open and update nano browser uis
  * @return nothing
  */
 /datum/nanoui/process(update = 0)
-	if (!src_object || !user)
+	if (QDELETED(src_object) || QDELETED(user))
 		close()
 		return