Add newitem module: highlight freshly-acquired bag items

New module built on ClassicAPI's C_NewItems + BAG_NEW_ITEMS_UPDATED.
Glows bag slots (bags 0-4) holding items acquired since login, keyed on
item GUID so the flag survives rearranging. Hovering an item
acknowledges it (RemoveNewItem); closing the bags clears the rest via
ClearAll. Glow is UI-ActionButton-Border, sized off the slot width so it
tracks the icon_size config.

To stay decoupled from the bag frames, the bag module now broadcasts a
reusable "bag:closed" event through pfUI.events from its OnHide (carrying
the container so subscribers can tell backpack from bank), guarded so the
initial setup Hide() doesn't fire a phantom close.

Config: appearance.bags.newitem + newitem_color, with GUI toggles.

init/modules.xml

@@ -79,4 +79,5 @@
   <Include file="..\modules\bgscore.lua"/>
   <Include file="..\modules\equipmentmanager.lua"/>
   <Include file="..\modules\loothistory.lua"/>
+  <Include file="..\modules\newitem.lua"/>
 </Ui>