fix(a11y): add aria-labels to chat core components (#21709)

Add aria-labels to close, back, and action buttons across:
- Controls/Controls.svelte: close chat controls button
- ChatControls/Embeds.svelte: close embed button
- Overview/Node.svelte: favorite toggle button
- Overview/View.svelte: back and close overview buttons
- ShortcutsModal.svelte: close button
- ShareChatModal.svelte: close button
- ToolServersModal.svelte: close button
- Placeholder/FolderTitle.svelte: folder icon picker, folder options menu

WCAG: 4.1.2 (Name, Role, Value)

src/lib/components/chat/Placeholder/FolderTitle.svelte

@@ -173,6 +173,7 @@
 				}}
 			>
 				<button
+					aria-label={$i18n.t('Change folder icon')}
 					class=" rounded-full bg-gray-50 dark:bg-gray-800 size-11 flex justify-center items-center"
 				>
 					{#if folder?.meta?.icon}
@@ -201,7 +202,7 @@
 					exportHandler();
 				}}
 			>
-				<button class="p-1.5 dark:hover:bg-gray-850 rounded-full touch-auto" on:click={(e) => {}}>
+				<button class="p-1.5 dark:hover:bg-gray-850 rounded-full touch-auto" aria-label={$i18n.t('Folder options')} on:click={(e) => {}}>
 					<EllipsisHorizontal className="size-4" strokeWidth="2.5" />
 				</button>
 			</FolderMenu>