Use ClassicAPI EventUtil for addon-load/login extension wiring

Replace hand-rolled ADDON_LOADED/PLAYER_LOGIN handlers with
EventUtil.ContinueOnAddOnLoaded / ContinueOnPlayerLogin, which fire
immediately if the event already happened -- removing the "we loaded before
the target addon and missed its ADDON_LOADED" workarounds.

- pfUI compat: ContinueOnAddOnLoaded("pfUI") + ContinueOnPlayerLogin; drops
  the missed-event fallback (login path still re-runs SetupCompatibility).
- MacroErrorUI / MacroLengthWarn: ContinueOnAddOnLoaded("Blizzard_MacroUI"),
  folding their manual "already loaded" checks.
- 9 Mouseover extensions (ag_UnitFrames, CT_RaidAssist, CT_UnitFrames,
  DiscordUnitFrames, Grid, NotGrid, Cursive, sRaidFrames, PerfectRaid):
  ContinueOnAddOnLoaded("<AddonName>", OnLoad). Since immediate-fire passes no
  event args, the old `arg1 == "X"` checks are replaced by the addon-name gate
  (global guards kept where present); also removes the buggy
  UnregisterEvent("ADDON_LOADED", "Onload") no-ops that never fired.

Addon names match file names; drops support for renamed folders (e.g. -master).

Extensions/Mouseover/NotGrid.lua

@@ -8,7 +8,6 @@ local CleveRoids = _G.CleveRoids or {}
 local CreateFrames = nil
 
 local Extension = CleveRoids.RegisterExtension("NotGrid")
-Extension.RegisterEvent("ADDON_LOADED", "OnLoad")
 
 function Extension.OnEnter()
     CleveRoids.SetMouseoverFrom("ngrid", this.unit)
@@ -48,7 +47,6 @@ function Extension.OnLoad()
     CreateFrames = NotGrid.CreateFrames
     NotGrid.CreateFrames = CleveRoids.NotGrid_CreateFrames
 
-    Extension.UnregisterEvent("ADDON_LOADED", "Onload")
 end
 
-_G["CleveRoids"] = CleveRoids
+EventUtil.ContinueOnAddOnLoaded("NotGrid", Extension.OnLoad)