feat: responsive mobile layout for monitoring dashboard

Redesign the UI to work on mobile/portrait viewports using CSS media
queries at max-width 768px:

- Host rows stack vertically: info (name, latency, status) on top,
  sparkline chart full-width below
- Summary stats line wraps properly with hidden pipe separators
- Header stacks title and controls vertically
- Pause button and controls sized appropriately for touch
- Pin button repositioned for mobile touch targets
- Footer legend wraps cleanly

Desktop layout remains pixel-identical — all changes are scoped to the
@media (max-width: 768px) query in styles.css only.

Refs #2

README.md

@@ -102,9 +102,6 @@ dist/
   false outage)
 - Clickable service URLs
 - Canvas-based sparkline rendering with devicePixelRatio scaling
-- Mobile detection: viewports narrower than 768px show a friendly "not yet
-  available on mobile" message instead of the monitoring UI (no polling or
-  network requests on mobile)
 - Zero runtime dependencies: all resources bundled into build artifacts
 
 ## Deployment
@@ -128,8 +125,6 @@ properties.
 
 ## Limitations
 
-- **Mobile**: Viewports below 768px wide show a static "not yet available"
-  message. The full monitoring UI requires a desktop-width browser.
 - **CORS**: Some hosts may block cross-origin HEAD requests. The app uses
   `no-cors` mode which allows the request but provides opaque responses. Latency
   is still measurable based on request timing.

src/main.js

@@ -1126,46 +1126,11 @@ function handleResize(state) {
     });
 }
 
-// --- Mobile Detection --------------------------------------------------------
-
-const MOBILE_BREAKPOINT = 768;
-
-function isMobileViewport() {
-    return window.innerWidth < MOBILE_BREAKPOINT;
-}
-
-function buildMobileUI() {
-    const app = document.getElementById("app");
-    app.innerHTML = `
-    <div class="mx-auto px-[5%] py-8">
-      <header class="mb-8">
-        <h1 class="text-3xl font-bold text-white"><a href="https://git.eeqj.de/sneak/netwatch" target="_blank" rel="noopener" class="underline decoration-dashed decoration-gray-500 underline-offset-4">NetWatch</a> by <a href="https://sneak.berlin" target="_blank" rel="noopener" class="text-blue-400 underline hover:text-blue-300">@sneak</a></h1>
-        <p class="text-gray-400 text-sm mt-2">Real-time network latency monitor</p>
-      </header>
-      <div class="flex items-center justify-center min-h-[60vh]">
-        <div class="bg-gray-800/70 border border-gray-700/50 rounded-lg p-8 max-w-md text-center">
-          <p class="text-4xl mb-4">📡</p>
-          <p class="text-xl font-semibold text-white mb-2">Not yet available on mobile</p>
-          <p class="text-gray-400 text-sm">NetWatch requires a wider viewport to display latency charts and monitoring data. Please visit on a desktop browser.</p>
-        </div>
-      </div>
-      <footer class="mt-8 text-center text-gray-600 text-xs">
-        <p><a href="https://git.eeqj.de/sneak/netwatch/commit/${__COMMIT_FULL__}" target="_blank" rel="noopener" class="text-gray-600 hover:text-gray-400">${__COMMIT_HASH__}</a></p>
-      </footer>
-    </div>`;
-}
-
 // --- Bootstrap ---------------------------------------------------------------
 
 async function init() {
     log.info("NetWatch starting");
 
-    if (isMobileViewport()) {
-        log.info("Mobile viewport detected — skipping monitoring");
-        buildMobileUI();
-        return;
-    }
-
     // Probe common gateway IPs to find the local router
     const gateway = await detectGateway();
     const localHosts = [LOCAL_CPE];