feat(ui5-list): add live region announcement for item selection

[NakataCode]

Problem:

• When a user selects or deselects a list item with a mouse click, screen readers get no immediate feedback. They only discover the selection state when navigating back to the item, because the AT reads aria-selected on focus.

Solution:

• Call announce() (InvisibleMessage) with a polite live region announcement immediately after a selection change succeeds. The text is "Selected" or "Not Selected" using the existing i18n strings LIST_ITEM_SELECTED / LIST_ITEM_NOT_SELECTED.

---

What's covered:

• All selectable modes: Single, SingleStart, SingleEnd, SingleAuto, Multiple
• Mouse clicks and keyboard (Space/Enter)
• SingleAuto arrow-key navigation (goes through the same onSelectionRequested path)
• No announcement when selectionMode="None"
• No announcement when the consumer prevents the selection-change event
• Delete mode is naturally excluded — it never toggles selected

[ui5-webcomponents-bot]

🚀 Deployed on https://pr-13440--ui5-webcomponents-preview.netlify.app

[NakataCode]

Code review

Found 2 issues:

1. InvisibleMessageMode is imported as a value instead of import type + string literal (packages/base/AGENTS.md says: "BAD - imports the enum object (runtime overhead) / GOOD - import type only (no runtime overhead)" and "BAD - runtime enum access / GOOD - string comparison")

webcomponents/packages/main/src/List.ts

Lines 39 to 42 in d8200f0

	} from "@ui5/webcomponents-base/dist/util/AccessibilityTextsHelper.js";
	import getNormalizedTarget from "@ui5/webcomponents-base/dist/util/getNormalizedTarget.js";
	import announce from "@ui5/webcomponents-base/dist/util/InvisibleMessage.js";
	import InvisibleMessageMode from "@ui5/webcomponents-base/dist/types/InvisibleMessageMode.js";

The fix: import type InvisibleMessageMode from "..." and replace InvisibleMessageMode.Polite with "Polite".

2. The announce() call fires in Delete selectionMode, producing a misleading "Selected" or "Not Selected" announcement when the user presses the delete button. handleDelete returns true, which sets selectionChange = true, which triggers the else branch — but the @event("selection-change") JSDoc explicitly lists only Single, SingleStart, SingleEnd, and Multiple modes, not Delete. In Delete mode, item.selected is irrelevant to the user action.

webcomponents/packages/main/src/List.ts

Lines 921 to 932 in d8200f0

	});
	if (changePrevented) {
	this._revertSelection(previouslySelectedItems);
	} else {
	const item = e.detail.item;
	const selectedText = item.selected
	? List.i18nBundle.getText(LIST_ITEM_SELECTED)
	: List.i18nBundle.getText(LIST_ITEM_NOT_SELECTED);
	announce(selectedText, InvisibleMessageMode.Polite);
	}
	}
	}

The fix: guard the announce() call to exclude Delete mode (e.g. check this.selectionMode !== ListSelectionMode.Delete).

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