fix: wait for builds to drain before restart

[dobrac]

Note

Introduce ServerStore.Wait and update orchestrator shutdown to mark draining, wait for propagation, then wait for template builds to finish before closing services.

• Orchestrator shutdown:
  • Mark service as Draining, then pause 15s (non-local) for propagation.
  • If template manager is running, call tmpl.Wait(ctx) before closing services; log errors and affect exit status.
• Template manager (ServerStore):
  • Add Wait(ctx) to block until in-flight builds finish and perform non-local delay checks.
  • Simplify Close(ctx) to only close internal resources and return aggregated errors.

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