Ahelp and Mhelp QOL (#24597)

* Bound ahelp/mhelp replies more tightly to their ticket.

* Hardened PMs further against missing data.

* Support expanding Discord notifications for ahelp/mhelp.

Functionality changes:
* Informs the user when their ticket is reopened.
* Informs other mentors/admins when tickets are converted.
* Discord messages now get a "Ticket 3, " or similar prefix.
  Not useful by itself, but will be with the following PR.

Code changes:
* When you create a ticket, you get the ticket object back.
* checkForTicket now allows you to fetch a ticket by number, and falls
  back to searching for open tickets if the ticket isn't found.
* Corrected and simplified the logic for adding PMs to tickets.
* Responses are now added through the ticket system, not the tickets
  directly.

code/modules/client/client_procs.dm

@@ -105,7 +105,7 @@
 	if(href_list["priv_msg"])
 		var/ckey_txt = href_list["priv_msg"]
 
-		cmd_admin_pm(ckey_txt, null, href_list["type"])
+		cmd_admin_pm(ckey_txt, null, href_list["type"], ticket_id = text2num(href_list["ticket_id"]))
 		return
 
 	if(href_list["discord_msg"])