Plugin select dropdowns (e.g. ep_headings) don't return focus to the pad after selection

[JohnMcLear]

Selecting an option from a plugin-provided toolbar dropdown (reproduced with ep_headings → "Heading 1") leaves keyboard focus on the dropdown itself rather than returning it to the pad editor. Users who navigated in with keyboard have to click back into the pad to resume typing.

Reproduction

1. Enable ep_headings2 plugin.
2. Open a pad.
3. Click the heading dropdown in the toolbar.
4. Click "Heading 1".
5. Start typing — keystrokes go nowhere (focus is still on the dropdown).

Expected

After applying a block-style action via a toolbar dropdown, focus should return to the pad editor (the inner ace iframe's editable) so the user can keep typing.

Notes

• Unrelated to fix(a11y): dialog semantics, focus management, icon labels, html lang #7584 (a11y dialogs PR). That PR handles focus restoration for popup dialogs opened via toggleDropDown (Settings, Import/Export, Embed, Users, etc.). Plugin-provided <select>-style dropdowns go through a different path and aren't covered.
• Fix likely needs to call pad.ace.ace_focus() after a plugin dropdown's change event fires — either in the core toolbar select handler or per-plugin.

Discovered while testing #7584.

[JohnMcLear]

I thought I'd fixed this but turns out no..