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.

env/translations_enUS.lua

@@ -411,6 +411,7 @@ pfUI_translation["enUS"] = {
   ["Highlight Equipped Items"] = nil,
   ["Highlight Not Usable Spells"] = nil,
   ["Highlight Out Of Mana Spells"] = nil,
+  ["Highlight New Items"] = nil,
   ["Highlight Out Of Range Spells"] = nil,
   ["Highlight Settings That Require Reload"] = nil,
   ["Highlight Unusable Items"] = nil,
@@ -529,6 +530,7 @@ pfUI_translation["enUS"] = {
   ["Network Latency"] = nil,
   ["Network Up"] = nil,
   ["New entry:"] = nil,
+  ["New Item Color"] = nil,
   ["NEW TIMER"] = nil,
   ["Next"] = nil,
   ["Next Memory Cleanup"] = nil,