Adopt ClassicAPI in Conditionals: item cooldown, stealth, nameplates

- GetItemCooldownCached: resolve via ClassicAPI GetItemCooldown (by item
  id/name) instead of FindItemLocation + nampower GetItemIdCooldown +
  link parsing; equipment slots (1-19) still query the inventory slot.
- [stealth]/[nostealth] and [stl]/[nostl], and the Rogue branch of
  GetCurrentShapeshiftIndex, now use ClassicAPI IsStealthed() (covers
  Rogue Stealth + Druid Prowl) instead of class-gated localized buff
  lookups. Note: [nostealth] is now true for non-stealth classes.
- CountEnemiesMatching nameplate scan uses C_NamePlate.GetNamePlateGUIDs()
  instead of walking WorldFrame children and extracting GUIDs via
  pcall(frame.GetName).
- Add ClassicAPI.IsStealthed / GetNamePlateGUIDs wrappers.

ClassicAPI.lua

@@ -118,3 +118,22 @@ end
 function API.GetActionInfo(slot)
     return GetActionInfo(slot)
 end
+
+--------------------------------------------------------------------------------
+-- State
+--------------------------------------------------------------------------------
+
+-- True if the player is in Stealth (Rogue) or Prowl (Druid).
+function API.IsStealthed()
+    return IsStealthed()
+end
+
+--------------------------------------------------------------------------------
+-- NamePlate
+--------------------------------------------------------------------------------
+
+-- 1-based table of GUID strings (0x... format) for every unit with an allocated
+-- nameplate, including default vanilla nameplates. Order isn't stable.
+function API.GetNamePlateGUIDs()
+    return C_NamePlate.GetNamePlateGUIDs()
+end