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

src/styles.css

@@ -21,3 +21,96 @@ body {
         rgba(255, 255, 255, 0) 100%
     );
 }
+
+/* ---- Mobile responsive layout (portrait / narrow viewports) ---- */
+@media (max-width: 768px) {
+    /* Header: stack title and controls vertically */
+    header .flex.items-center.justify-between {
+        flex-direction: column;
+        align-items: flex-start !important;
+        gap: 1rem;
+    }
+
+    header .flex.flex-col.items-end {
+        align-items: flex-start !important;
+        flex-direction: row;
+        flex-wrap: wrap;
+        gap: 0.75rem;
+    }
+
+    /* Pause button: smaller on mobile */
+    #pause-btn {
+        padding: 0.5rem 1rem;
+    }
+
+    #pause-btn svg {
+        width: 1.25rem;
+        height: 1.25rem;
+    }
+
+    #pause-text {
+        font-size: 0.875rem;
+    }
+
+    /* Summary box: wrap into a grid for readability */
+    #summary {
+        display: flex;
+        flex-wrap: wrap;
+        gap: 0.25rem 0.5rem;
+        justify-content: center;
+        line-height: 1.6;
+    }
+
+    /* Hide the pipe separators on mobile */
+    #summary .text-gray-600.mx-3 {
+        display: none;
+    }
+
+    /* Host row: stack vertically */
+    .host-row .flex.items-center.gap-4 {
+        flex-direction: column;
+        align-items: stretch !important;
+        gap: 0.5rem;
+    }
+
+    /* Info section: full width, remove fixed width */
+    .host-row .w-\[420px\] {
+        width: 100% !important;
+        display: grid;
+        grid-template-columns: 1fr auto;
+        align-items: center;
+    }
+
+    /* Host name row with dot */
+    .host-row .flex.items-center.gap-2.min-w-\[200px\] {
+        min-width: 0;
+    }
+
+    /* Latency value: slightly smaller on mobile */
+    .host-row .latency-value {
+        font-size: 1.875rem;
+        line-height: 2.25rem;
+    }
+
+    /* Sparkline: full width below the info */
+    .host-row .sparkline-container {
+        width: 100%;
+        flex-shrink: 0;
+    }
+
+    /* Pin button: inline with the host info */
+    .host-row .pin-btn {
+        position: absolute;
+        right: 0.5rem;
+        top: 0.5rem;
+    }
+
+    .host-row {
+        position: relative;
+    }
+
+    /* Footer legend: wrap nicely */
+    footer p {
+        line-height: 1.8;
+    }
+}