feat(ui): add centered 'Add Item' button to all storage locations

- Added persistent '+ Add Item' button at bottom of each storage location
- Button is centered and always visible (whether location has 0 or many items)
- Removed redundant '+ Add' button from storage location header (kept trash button)
- Reverted empty state to simple message instead of special button
- Added CSS for .rpg-storage-add-item-container to center button with margin
- Matches UI pattern from On Person and Assets tabs
- Removed debug logging from inventoryActions.js

style.css

@@ -4080,6 +4080,12 @@ body:has(.rpg-panel.rpg-position-left) #sheld {
     display: none;
 }
 
+.rpg-storage-add-item-container {
+    display: flex;
+    justify-content: center;
+    margin-top: 0.75rem;
+}
+
 /* Buttons */
 .rpg-inventory-edit-btn,
 .rpg-inventory-add-btn,