Export app, process and log telemetry when OTEL_ENABLED is set

Adds tavolo.active_users and tavolo.ongoing_games gauges, process/CPython
metrics via opentelemetry-instrumentation-system-metrics and OTLP log
export. The game store tracks ongoing matches (Redis sorted set, in-memory
set) and the session stores expose live counts for the gauges; a poller
refreshes them since metric callbacks cannot await the stores.

server/tests/test_config.py

@@ -164,6 +164,19 @@ class OTelSettingsTests(unittest.TestCase):
         settings = _settings({"OTEL_EXCLUDED_PATHS": "/api/health, /metrics"})
         self.assertEqual(("/api/health", "/metrics"), settings.otel_excluded_paths)
 
+    def test_otel_interval_defaults(self):
+        settings = _settings({})
+        self.assertEqual(60000, settings.otel_metric_export_interval_millis)
+        self.assertEqual(15, settings.otel_metrics_poll_interval_seconds)
+
+    def test_otel_intervals_parse(self):
+        settings = _settings({
+            "OTEL_METRIC_EXPORT_INTERVAL_MILLIS": "5000",
+            "OTEL_METRICS_POLL_INTERVAL_SECONDS": "3",
+        })
+        self.assertEqual(5000, settings.otel_metric_export_interval_millis)
+        self.assertEqual(3, settings.otel_metrics_poll_interval_seconds)
+
 
 if __name__ == "__main__":
     unittest.main()