fix(telemetry): review fixes — flush/shutdown ordering, session retirement, whole-exporter passthrough

Three review findings, each pinned by a red test first:

- The OTel backend retains the latest turn-boundary flush promise and
  shutdown() awaits it before provider.shutdown(): the SDK's
  concurrent-flush guard makes the shutdown-internal flush return early
  while one is in flight, silently dropping everything enqueued after
  the flush snapshot (including the coordinator's dispose-time shutdown
  markers).
- The coordinator retires sessions from the adopted set on
  session/disposed (mirroring the persistence coordinator): a long-lived
  backend no longer retains closed sessions and their event logs, and
  final unload no longer stamps shutdown markers for dead sessions.
- The exporter config passes through whole to OTLPLogExporter and its
  type/JSDoc now advertise the full OTLPExporterNodeConfigBase shape:
  rebuilding url/headers only silently dropped documented SDK options
  (timeoutMillis, compression, keepAlive, ...).

packages/telemetry/session-telemetry-otel/package.json

@@ -30,6 +30,7 @@
     "@opentelemetry/api": "^1.9.1",
     "@opentelemetry/api-logs": "^0.220.0",
     "@opentelemetry/exporter-logs-otlp-http": "^0.220.0",
+    "@opentelemetry/otlp-exporter-base": "^0.220.0",
     "@opentelemetry/resources": "^2.9.0",
     "@opentelemetry/sdk-logs": "^0.220.0",
     "schemastery": "^3.18.0"