test: pin app-footer mobile/desktop visibility; trim comment

Add a Playwright regression test asserting .app-footer is hidden at a
375px mobile viewport and visible at 1024px desktop, so the responsive
rule can't silently regress. Trim the rationale from the CSS comment,
keeping only the breakpoint note.

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

Author: dobby-coder[bot]

src/routes/(app)/+layout.svelte

@@ -75,8 +75,7 @@
         }
     }
 
-    /* Hide the footer on mobile / small viewports — it costs too much screen
-       real estate there. Mirrors the Header's 768px desktop breakpoint. */
+    /* Match Header's 768px desktop breakpoint. */
     @media only screen and (max-width: 767.98px) {
         .app-footer {
             display: none;

tests/app-footer-responsive.test.ts

@@ -0,0 +1,19 @@
+import { expect, test } from '@playwright/test'
+
+// Regression test for hiding the compact app footer on mobile viewports
+// (issue encryption4all/postguard-website#279). The footer lives in the (app)
+// layout and is hidden below Header's 768px desktop breakpoint, where it cost
+// too much screen real estate. It must stay visible on desktop.
+const FOOTER = '.app-footer'
+
+test('app footer is hidden on a mobile viewport', async ({ page }) => {
+    await page.setViewportSize({ width: 375, height: 812 })
+    await page.goto('/fileshare/')
+    await expect(page.locator(FOOTER)).toBeHidden()
+})
+
+test('app footer is visible on a desktop viewport', async ({ page }) => {
+    await page.setViewportSize({ width: 1024, height: 768 })
+    await page.goto('/fileshare/')
+    await expect(page.locator(FOOTER)).toBeVisible()
+})