fix(a11y): add aria-labels to chat message components (#21708)

Add aria-labels, aria-expanded, and semantic improvements to:
- RateComment: close button, rating scale, feedback textarea
- Citations: toggle button with count, source item buttons
- Source/SourceToken: contextual aria-labels for citation buttons
- StatusHistory: toggle button with expanded state
- WebSearchResults: descriptive favicon alt text
- FollowUps: convert div to button element
- RegenerateMenu: submit suggestion button
- FloatingButtons: action buttons, input field, submit button
- CitationModal: close button

WCAG: 4.1.2 (Name, Role, Value), 2.1.1 (Keyboard), 1.1.1 (Non-text Content)

src/lib/components/chat/Messages/Markdown/Source.svelte

@@ -1,6 +1,9 @@
 <script lang="ts">
+	import { getContext } from 'svelte';
 	import { decodeString } from '$lib/utils';
 
+	const i18n = getContext('i18n');
+
 	export let id;
 
 	export let title: string = 'N/A';
@@ -37,6 +40,7 @@
 
 {#if title !== 'N/A'}
 	<button
+		aria-label={$i18n.t('View source: {{title}}', { title: formattedTitle(decodeString(title)) })}
 		class="text-[10px] w-fit translate-y-[2px] px-2 py-0.5 dark:bg-white/5 dark:text-white/80 dark:hover:text-white bg-gray-50 text-black/80 hover:text-black transition rounded-xl"
 		on:click={() => {
 			onClick(id);

src/lib/components/chat/Messages/Markdown/SourceToken.svelte

@@ -48,6 +48,7 @@
 		<LinkPreview.Root openDelay={0} bind:open={openPreview}>
 			<LinkPreview.Trigger>
 				<button
+					aria-label={`${getDisplayTitle(formattedTitle(decodeString(sourceIds[token.ids[0] - 1])))} +${(token?.ids ?? []).length - 1} more sources`}
 					class="text-[10px] w-fit translate-y-[2px] px-2 py-0.5 dark:bg-white/5 dark:text-white/80 dark:hover:text-white bg-gray-50 text-black/80 hover:text-black transition rounded-xl"
 					on:click={() => {
 						openPreview = !openPreview;