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/README.md

@@ -8,7 +8,7 @@ The telemetry seam: the CAPTURE side of session-event reporting, behind a backen
 
 ## Capture points
 
-The coordinator registers, all through the composing fiber's effects: `session/created` (adopt: record the header, read the log back through the projection — seed events from fork/resume never re-emit on the firehose), `session/event` (project, deep-copy, redact, hand off; zero I/O), `session/flush` (forward the optional `flush()` hint and return void — the loop's awaited parallel must never wait on telemetry), `agent/error` (the one live-bus relay; turn-enclosure structurally bars those errors from the log), a dispose effect (per adopted session emit its `shutdown` operational record, then await the backend's `shutdown()`; failures warn instead of throwing), and an adoption sweep of `ctx.sessions.list()` (a hot reload does not replay `session/created`).
+The coordinator registers, all through the composing fiber's effects: `session/created` (adopt: record the header, read the log back through the projection — seed events from fork/resume never re-emit on the firehose), `session/event` (project, deep-copy, redact, hand off; zero I/O), `session/flush` (forward the optional `flush()` hint and return void — the loop's awaited parallel must never wait on telemetry), `session/disposed` (retire: release the adopted entry so a long-lived backend neither retains closed sessions nor stamps dispose-time markers for them), `agent/error` (the one live-bus relay; turn-enclosure structurally bars those errors from the log), a dispose effect (per still-adopted session emit its `shutdown` operational record, then await the backend's `shutdown()`; failures warn instead of throwing), and an adoption sweep of `ctx.sessions.list()` (a hot reload does not replay `session/created`).
 
 ## The redact waterfall