Split worker trace cleanup

[yvette-carlisle]

Summary

• Split worker trace expiry cleanup helpers into apps/elf-worker/src/worker/trace_jobs/cleanup.rs.
• Preserve the existing worker::purge_expired_* call surface through the trace_jobs re-export.
• Keep cleanup SQL, binding, logging, and return behavior unchanged.

Validation

• cargo make fmt-rust
• cargo check -p elf-worker --all-targets --all-features
• cargo make fmt-rust-check
• cargo make check-rust
• cargo make lint-vstyle
• git diff --check
• cargo make lint-rust
• cargo make test-rust
• cargo make check
• cargo make test-rust-integration
• cargo make check-trace-gate
• staged skeptic review: pass, no blockers or risks