Observability + warming guardrails (Codex)

* client_error details, not just a count: new client_errors table + POST
  /api/client-error (reason/path/user-agent/time) + GET /api/admin/client-errors.
  The boot-seatbelt beacon now sends the reason + path (once per page); the admin
  Overview lists the recent errors so we can tell chunk vs SW vs API vs JS — the
  truth meter for the next day as the new SW propagates.
* Deploy warming now also hits the shell, routes (/play /account /admin), SW,
  version.json, word lists, and icons/logo/font — not just immutable chunks.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/app.html

@@ -38,17 +38,22 @@
       // screen. Show a calm recovery card if the app hasn't mounted, and reload
       // once on a chunk/preload failure (e.g. a just-deployed hashed chunk).
       (function () {
-        function showBoot() {
+        var sent = false;
+        function report(reason) {
+          if (sent) return; sent = true;             // one beacon per page
+          try {
+            var b = new Blob([JSON.stringify({ reason: String(reason || 'unknown').slice(0, 300),
+                                               path: location.pathname })], { type: 'application/json' });
+            navigator.sendBeacon && navigator.sendBeacon('/api/client-error', b);
+          } catch (e) { /* best-effort telemetry */ }
+        }
+        function showBoot(reason) {
           if (window.__ubMounted) return;            // app is running; in-app handles it
           var el = document.getElementById('boot-fallback');
           if (el) el.style.display = 'flex';
-          try {
-            var b = new Blob([JSON.stringify({ kind: 'client_error', visitor: 'e' + Math.random().toString(36).slice(2) })],
-                             { type: 'application/json' });
-            navigator.sendBeacon && navigator.sendBeacon('/api/events', b);
-          } catch (e) { /* best-effort telemetry */ }
+          report(reason);
         }
-        var timer = setTimeout(showBoot, 10000);
+        var timer = setTimeout(function () { showBoot('boot-timeout'); }, 10000);
         // Svelte calls this once it has mounted (see +layout.svelte).
         window.__ubBooted = function () {
           window.__ubMounted = true;
@@ -58,6 +63,7 @@
           try { sessionStorage.removeItem('ub_reloaded'); } catch (e) {}
         };
         addEventListener('vite:preloadError', function (e) {
+          report('preloadError: ' + ((e && e.payload && e.payload.message) || ''));
           try {
             if (!sessionStorage.getItem('ub_reloaded')) {
               sessionStorage.setItem('ub_reloaded', '1');
@@ -66,8 +72,12 @@
             }
           } catch (err) { /* ignore */ }
         });
-        addEventListener('error', showBoot);
-        addEventListener('unhandledrejection', showBoot);
+        addEventListener('error', function (e) {
+          showBoot(e && (e.message || (e.error && e.error.message)) || 'error');
+        });
+        addEventListener('unhandledrejection', function (e) {
+          showBoot(e && e.reason && (e.reason.message || String(e.reason)) || 'rejection');
+        });
       })();
     </script>
   </head>