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.spec.ts

@@ -0,0 +1,36 @@
+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/);
+	});
+});