Updates href uses for 516 (#88699)

## About The Pull Request

Was just scrolling through the Paradise github since they seem to have
more work done for 516 to see if there's anything I can port over, found
this and thought why not.

Ports parts of https://github.com/ParadiseSS13/Paradise/pull/25105
Specifically, updaing all hrefs to use the internal ``byond://``, and
adding it to grep.

## Why It's Good For The Game

More work towards 516.

## Changelog

Nothing player-facing.

code/modules/mob/dead/observer/observer.dm

@@ -436,7 +436,7 @@ This is the proc mobs get to turn into a ghost. Forked from ghostize due to comp
 				A.add_overlay(source)
 				source.layer = old_layer
 				source.plane = old_plane
-	to_chat(src, span_ghostalert("<a href=?src=[REF(src)];reenter=1>(Click to re-enter)</a>"))
+	to_chat(src, span_ghostalert("<a href=byond://?src=[REF(src)];reenter=1>(Click to re-enter)</a>"))
 	if(sound)
 		SEND_SOUND(src, sound(sound))