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/ResponseMessage/WebSearchResults.svelte

@@ -67,7 +67,7 @@
 						<div class="w-fit">
 							<img
 								src="https://www.google.com/s2/favicons?sz=32&domain={item.link}"
-								alt="favicon"
+								alt="{item?.title ?? item.link} favicon"
 								class="size-3.5"
 							/>
 						</div>
@@ -107,7 +107,7 @@
 						<div class="w-fit">
 							<img
 								src="https://www.google.com/s2/favicons?sz=32&domain={url}"
-								alt="favicon"
+								alt="{url} favicon"
 								class="size-3.5"
 							/>
 						</div>