Edit Skill dialog: Save button is black and the close button is missing

## Problem

In **AI → Skills**, the **Edit Skill** dialog (opened from a skill's menu):

1. renders the **Save** button black instead of the primary blue used by other dialogs;
2. has no **X** close button in the top-right corner of the header.

## Cause

`client/src/pages/automation/ai/skills/components/AiSkillEditDialog.tsx` is built on the `AlertDialog` primitives. `AlertDialogAction` uses the shadcn dark default styling instead of the ByteChef `Button`, and alert dialogs have no close button. Other skill dialogs (e.g. `AiSkillWriteDialog`) use `Dialog` with the ByteChef `Button`.

## Expected

The dialog matches the other dialogs: a primary **Save** button, an outline **Cancel** button, and a `DialogCloseButton` next to the title.