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.

modules/bags.lua

@@ -337,6 +337,7 @@ pfUI:RegisterModule("bags", function ()
     local chat = pfUI.chat and ( object == "bank" and pfUI.chat.left or pfUI.chat.right) or nil
 
     frame:SetScript("OnShow", function()
+      frame.opened = true
       if C.appearance.bags.hidechat == "1" and chat and chat:IsVisible() then
         frame.chatWasOpen = true
         chat:Hide()
@@ -355,6 +356,10 @@ pfUI:RegisterModule("bags", function ()
       end
       pfUI.bag:CreateBags(object)
       PlaySound("INTERFACESOUND_BACKPACKCLOSE")
+      if frame.opened then
+        frame.opened = nil
+        pfUI.events:TriggerEvent("bag:closed", object)
+      end
     end)
   end