feat: UI improvements & tests

Improves the chat sidebar search component by adding a "search" type to the input for better mobile keyboard support and screen reader accessibility.
Also, adds a story to test the focus state of the search input.
Introduces new markdown fixtures for storybook.

Author: allozaur

tools/server/webui/src/lib/components/app/chat/ChatSidebar/ChatSidebarSearch.svelte

@@ -22,5 +22,6 @@
 	<Search
 		class="text-muted-foreground absolute left-3 top-1/2 h-4 w-4 -translate-y-1/2 transform"
 	/>
-	<Input bind:value {placeholder} class="pl-10" oninput={handleInput} />
+	
+	<Input bind:value type="search" {placeholder} class="pl-10" oninput={handleInput} />
 </div>

tools/server/webui/src/stories/ChatSidebarSearch.stories.svelte

@@ -13,6 +13,10 @@
 
 <Story name="Default" args={{ class: 'w-80' }} />
 
+<Story name="Focus" args={{ class: 'w-80' }} play={({ canvasElement }) => {
+	canvasElement.querySelector('input')?.focus();
+}}/>
+
 <Story
 	name="WithValue"
 	args={{