fix(a11y): improve model selector accessibility with proper listbox/option pattern (#21706)

- Replace incorrect aria-roledescription='model-item' with role='option' and aria-selected on ModelItem.svelte. The previous attribute was not a valid ARIA role description and provided no useful information to screen readers.

- Add contextual aria-label to each model item button (e.g. 'Select GPT-4 model') instead of just the raw model name, making the action clear to screen reader users.

- Add role='listbox' and aria-label='Available models' to the scrollable model list container in Selector.svelte so screen readers announce the container's purpose and navigate items correctly.

- Make the model selector trigger button's aria-label dynamic: it now announces 'Selected model: GPT-4' when a model is selected, falling back to 'Select a model' when nothing is selected.

- Add aria-label to the eject (unload) button in ModelItem.svelte so screen readers announce its purpose.

- Add aria-label to the cancel download button in Selector.svelte with the specific model name being canceled.

- Improve model profile image alt text from generic 'Model' to contextual '{{modelName}} profile image'.

src/lib/components/chat/ModelSelector/ModelItem.svelte

@@ -44,8 +44,9 @@
 </script>
 
 <button
-	aria-roledescription="model-item"
-	aria-label={item.label}
+	role="option"
+	aria-selected={value === item.value}
+	aria-label={$i18n.t('Select {{modelName}} model', { modelName: item.label })}
 	class="flex group/item w-full text-left font-medium line-clamp-1 select-none items-center rounded-button py-2 pl-3 pr-1.5 text-sm text-gray-700 dark:text-gray-100 outline-hidden transition-all duration-75 hover:bg-gray-100 dark:hover:bg-gray-800 rounded-xl cursor-pointer data-highlighted:bg-muted {index ===
 	selectedModelIdx
 		? 'bg-gray-100 dark:bg-gray-800 group-hover:bg-transparent'
@@ -78,7 +79,7 @@
 				<Tooltip content={$user?.role === 'admin' ? (item?.value ?? '') : ''} placement="top-start">
 					<img
 						src={`${WEBUI_API_BASE_URL}/models/model/profile/image?id=${item.model.id}&lang=${$i18n.language}`}
-						alt="Model"
+						alt={$i18n.t('{{modelName}} profile image', { modelName: item.label })}
 						class="rounded-full size-5 flex items-center"
 						loading="lazy"
 					/>
@@ -235,6 +236,7 @@
 			>
 				<button
 					class="flex"
+					aria-label={$i18n.t('Eject model')}
 					on:click={(e) => {
 						e.preventDefault();
 						e.stopPropagation();

src/lib/components/chat/ModelSelector/Selector.svelte

@@ -402,7 +402,7 @@
 		class="relative w-full {($settings?.highContrastMode ?? false)
 			? ''
 			: 'outline-hidden focus:outline-hidden'}"
-		aria-label={placeholder}
+		aria-label={selectedModel ? $i18n.t('Selected model: {{modelName}}', { modelName: selectedModel.label }) : placeholder}
 		id="model-selector-{id}-button"
 	>
 		<div
@@ -600,6 +600,8 @@
 					<!-- svelte-ignore a11y-no-static-element-interactions -->
 					<div
 						class="max-h-64 overflow-y-auto"
+						role="listbox"
+						aria-label={$i18n.t('Available models')}
 						bind:this={listContainer}
 						on:scroll={() => {
 							listScrollTop = listContainer.scrollTop;
@@ -681,6 +683,7 @@
 							<Tooltip content={$i18n.t('Cancel')}>
 								<button
 									class="text-gray-800 dark:text-gray-100"
+									aria-label={$i18n.t('Cancel download of {{model}}', { model: model })}
 									on:click={() => {
 										cancelModelPullHandler(model);
 									}}