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/MacroErrorUI.lua

@@ -1391,12 +1391,6 @@ end
 -- Extension Entry Points
 -- ============================================================================
 
-function Extension.OnAddonLoaded()
-    if arg1 == "Blizzard_MacroUI" then
-        InstallHooks()
-    end
-end
-
 function Extension.OnLoad()
     -- Skip if macro checker is disabled
     if CleveRoidMacros and CleveRoidMacros.macrocheck == 0 then return end
@@ -1404,13 +1398,9 @@ function Extension.OnLoad()
     -- Skip if SuperMacro is loaded (detected at load time)
     if SuperMacroFrame ~= nil then return end
 
-    -- Listen for macro UI loading
-    Extension.RegisterEvent("ADDON_LOADED", "OnAddonLoaded")
-
-    -- If MacroFrame already exists (unlikely but safe), hook immediately
-    if MacroFrame and MacroFrameText then
-        InstallHooks()
-    end
+    -- Install once Blizzard's macro UI is available (fires immediately if already
+    -- loaded), replacing the ADDON_LOADED listener + manual "already loaded" check.
+    EventUtil.ContinueOnAddOnLoaded("Blizzard_MacroUI", InstallHooks)
 end
 
 _G["CleveRoids"] = CleveRoids