Server: lifetime stats counters in a collapsed web UI section

New FrameStats (first_seen, device_wakes, photos_displayed,
photos_removed, battery_reports, recharge_cycles, ota_updates_applied,
config_saves), persisted alongside everything else in config.json.
Incremented at the existing route/photo_queue.py call sites that already
own each event -- no new instrumentation plumbing, no behavior depends
on these, purely informational. GET /api/stats serves them; the web UI
renders them into a native <details> "Stats" card (collapsed by default,
no JS needed for the expand/collapse), fetched once on page load like
the battery-history chart.

Verified: TestClient run through /frame/config (wakes + first_seen +
OTA-applied detection), /frame/battery (reports + recharge detection),
/api/config (saves); direct photo_queue.py unit checks for
advance/back/remove covering the "did the current photo actually
change" distinction (removing a queued-but-not-current photo bumps
photos_removed but not photos_displayed).

server/app/templates/index.html

@@ -105,6 +105,11 @@
         <input type="file" id="firmware-file" accept=".bin">
         <button type="button" class="secondary" id="firmware-upload">Upload firmware</button>
       </section>
+
+      <details class="card">
+        <summary class="card-title">Stats</summary>
+        <div id="stats-box"><p class="sub">Loading...</p></div>
+      </details>
     </div>
   </div>
 
@@ -609,8 +614,45 @@
       }
     }
 
+    function renderStats(stats) {
+      const el = document.getElementById('stats-box');
+      el.innerHTML = '';
+      const now = Date.now() / 1000;
+      const rows = [
+        ['Running since', stats.first_seen ? formatDuration(Math.max(0, now - stats.first_seen)) + ' ago' : 'never checked in'],
+        ['Wake cycles', stats.device_wakes],
+        ['Photos displayed', stats.photos_displayed],
+        ['Photos removed from rotation', stats.photos_removed],
+        ['Battery reports received', stats.battery_reports],
+        ['Battery recharge cycles', stats.recharge_cycles],
+        ['OTA updates applied', stats.ota_updates_applied],
+        ['Settings saved', stats.config_saves],
+      ];
+      for (const [label, value] of rows) {
+        const p = document.createElement('p');
+        p.className = 'sub';
+        p.textContent = `${label}: ${value}`;
+        el.appendChild(p);
+      }
+    }
+
+    async function loadStats() {
+      const el = document.getElementById('stats-box');
+      try {
+        const resp = await fetch('/api/stats');
+        if (!resp.ok) {
+          el.innerHTML = '<p class="sub">Could not load.</p>';
+          return;
+        }
+        renderStats(await resp.json());
+      } catch (e) {
+        el.innerHTML = '<p class="sub">Could not load.</p>';
+      }
+    }
+
     loadQueue();
     loadBatteryLog();
+    loadStats();
 
     // Redraw the canvas chart (and the "Last seen" alert color) with the
     // new theme's colors as soon as the toggle in the header is used --