perf(orchestrator): move export_summary into spawned task in persist_telemetry

## Context

`persist_telemetry()` calls `export_summary().await` on the reconciliation tick before spawning. The N+2 read lock acquisitions and full clone happen on the hot path.

## Proposed fix

Pass `TelemetryStore` clone into the spawned task, call `export_summary()` inside it.

Refs terraphim/terraphim-ai#539 (Gitea), Refs #523