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/requirements.txt

@@ -93,6 +93,8 @@ opentelemetry-api==1.45.0
     # via
     #   opentelemetry-exporter-http-transport
     #   opentelemetry-exporter-otlp-proto-http
+    #   opentelemetry-instrumentation
+    #   opentelemetry-instrumentation-system-metrics
     #   opentelemetry-sdk
     #   opentelemetry-semantic-conventions
 opentelemetry-exporter-http-transport[urllib3]==0.66b0
@@ -103,6 +105,10 @@ opentelemetry-exporter-otlp-proto-common==1.45.0
     # via opentelemetry-exporter-otlp-proto-http
 opentelemetry-exporter-otlp-proto-http==1.45.0
     # via kaya-otel
+opentelemetry-instrumentation==0.66b0
+    # via opentelemetry-instrumentation-system-metrics
+opentelemetry-instrumentation-system-metrics==0.66b0
+    # via tavolo-app (pyproject.toml)
 opentelemetry-proto==1.45.0
     # via
     #   opentelemetry-exporter-otlp-proto-common
@@ -113,11 +119,18 @@ opentelemetry-sdk==1.45.0
     #   opentelemetry-exporter-otlp-common
     #   opentelemetry-exporter-otlp-proto-http
 opentelemetry-semantic-conventions==0.66b0
-    # via opentelemetry-sdk
+    # via
+    #   opentelemetry-instrumentation
+    #   opentelemetry-instrumentation-system-metrics
+    #   opentelemetry-sdk
+packaging==26.3
+    # via opentelemetry-instrumentation
 protobuf==7.36.2
     # via
     #   googleapis-common-protos
     #   opentelemetry-proto
+psutil==7.2.2
+    # via opentelemetry-instrumentation-system-metrics
 pwo==0.1.2
     # via
     #   kaya-core
@@ -151,3 +164,5 @@ typing-extensions==4.16.0
     #   pwo
 urllib3==2.8.0
     # via opentelemetry-exporter-http-transport
+wrapt==2.5.0
+    # via opentelemetry-instrumentation