feat(search): add SmartModeToggle pill component (#739)

Toggle pill with aria-pressed, active/resting styles matching the
AND/OR operator button pattern, and mobile-expanded KI/Text labels.
4 vitest-browser-svelte specs (red/green).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/routes/search/SmartModeToggle.svelte

@@ -0,0 +1,38 @@
+<script lang="ts">
+import { m } from '$lib/paraglide/messages.js';
+
+let { smartMode = $bindable(false), onToggle }: { smartMode?: boolean; onToggle?: () => void } =
+	$props();
+
+const label = $derived(smartMode ? m.search_toggle_smart_label() : m.search_toggle_keyword_label());
+const labelSuffix = $derived(
+	smartMode ? m.search_toggle_smart_label_suffix() : m.search_toggle_keyword_label_suffix()
+);
+
+function toggle() {
+	smartMode = !smartMode;
+	onToggle?.();
+}
+</script>
+
+<button
+	type="button"
+	aria-pressed={smartMode}
+	onclick={toggle}
+	class="pointer-events-auto absolute top-1/2 right-2 flex -translate-y-1/2 cursor-pointer items-center gap-1.5 rounded-full px-2.5 py-1 text-[7.5px] font-bold uppercase outline-none focus-visible:ring-2 focus-visible:ring-brand-navy {smartMode
+		? 'border border-primary bg-primary text-primary-fg'
+		: 'border border-line bg-muted text-ink-2'}"
+>
+	<svg
+		aria-hidden="true"
+		viewBox="0 0 24 24"
+		fill="currentColor"
+		class="h-2.5 w-2.5"
+		xmlns="http://www.w3.org/2000/svg"
+	>
+		<path d="M12 2l2.09 6.26L20 10l-5.91 1.74L12 18l-2.09-6.26L4 10l5.91-1.74L12 2z" />
+	</svg>
+	<span>
+		{label}<span class="sm:hidden">{labelSuffix}</span>
+	</span>
+</button>

frontend/src/routes/search/SmartModeToggle.svelte.spec.ts

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+import { describe, expect, it, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import SmartModeToggle from './SmartModeToggle.svelte';
+
+afterEach(() => cleanup());
+
+describe('SmartModeToggle', () => {
+	it('renders aria-pressed="false" by default and toggles on click', async () => {
+		render(SmartModeToggle, { smartMode: false });
+		const btn = page.getByRole('button');
+		await expect.element(btn).toHaveAttribute('aria-pressed', 'false');
+		await btn.click();
+		await expect.element(btn).toHaveAttribute('aria-pressed', 'true');
+		await btn.click();
+		await expect.element(btn).toHaveAttribute('aria-pressed', 'false');
+	});
+
+	it('shows the smart label when smartMode is true', async () => {
+		render(SmartModeToggle, { smartMode: true });
+		const btn = page.getByRole('button');
+		await expect.element(btn).toHaveTextContent('KI');
+	});
+
+	it('shows the keyword label when smartMode is false', async () => {
+		render(SmartModeToggle, { smartMode: false });
+		const btn = page.getByRole('button');
+		await expect.element(btn).toHaveTextContent('Text');
+	});
+
+	it('applies the active pill style only in smart mode', async () => {
+		render(SmartModeToggle, { smartMode: true });
+		const btn = page.getByRole('button');
+		await expect.element(btn).toHaveClass(/bg-primary/);
+	});
+});