CountableItemEditDlg and caller window's now work as expected

[soL-KO]

Title: Improve Countable Item Dialog UX, auto-focus,

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

What is the current behaviour?

Previously, the CCountableItemEditDlg (the popup for splitting stackable items) lacked several Quality of Life features:

1. It didn't show the total stack size the player currently possessed.
2. The dialog would open unnecessarily even if the player only had exactly 1 item in the stack.
3. The input field was not automatically focused when the dialog opened, requiring the player to perform an extra mouse click just to edit the amount.

What is the new behaviour?

• The dialog now automatically populates and displays the item's maximum stack size.
• The dialog input field is automatically focused upon opening, allowing players to start typing the amount immediately.
• The dialog intelligently bypasses the prompt if the item count is exactly 1, executing the transaction instantly.

Why and how did I change this?

The primary goal was to improve the UX for handling stackable items.

Was AI used at some point for any part of this change? If so, what?

Yes. It did the pr layout and pretty much everything else.

Demo

N/A

Checklist

• I have performed a self-review of my own code.
• Where applicable, I have checked to make sure that this doesn't introduce incompatible behaviour with the official 1.298 server (e.g. unofficial opcodes or behavioural differences).
• I have checked to make sure that this change does not already exist in the codebase in some fashion (e.g. UI already implemented under a different name).