SMOODEV-2045: SDK self-emit is panic-proof (fix temporal-worker crashloop root cause)

[brentrager]

Root cause of the prod temporal-worker crashloop (SMOODEV-1988 self-emit; mitigated by disabling it in SMOODEV-2031): the OTLP export executed in a context with no Tokio reactor present, so the HTTP request panicked; under the workspace's panic = "abort" release profile that panic on the background path aborted the whole host process → crashloop (blocked eSign).

Fix: drive the export on a dedicated std::thread with its own runtime so a missing-reactor / auth-401 / unreachable-endpoint never panics or aborts the host. The SDK is now genuinely best-effort even when configured-but-unreachable.

Tests (new tests/self_emit_panic_safety.rs): configured_but_unauthorized_ingest_does_not_panic, unreachable_endpoint_export_does_not_panic — both pass. fmt/clippy/test green.

NOTE: this does NOT re-enable self-emit anywhere — SMOODEV-2031's SMOOAI_OBSERVABILITY_DISABLED stays. It makes the SDK safe so self-emit CAN be re-enabled after review.

🤖 Generated with Claude Code

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