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/Controls/Controls.svelte

@@ -22,6 +22,7 @@
 		<div class=" text-lg font-medium self-center font-primary">{$i18n.t('Chat Controls')}</div>
 		<button
 			class="self-center"
+			aria-label={$i18n.t('Close chat controls')}
 			on:click={() => {
 				dispatch('close');
 			}}