XY-817: [ELF prod P0] Add resumable batch ingest and backfill benchmark

[yvette-carlisle]

Summary

• add checkpointed, resumable ELF live-baseline backfill with stable source hashes and duplicate-source validation
• add bounded worker concurrency for benchmark outbox draining
• add Docker backfill profile, Makefile task, and markdown report backfill evidence

Verification

• cargo make fmt
• cargo check -p elf-eval --bin live_baseline_elf
• bash -n scripts/live-baseline-benchmark.sh
• bash -n scripts/live-baseline-report-to-md.sh
• ELF Docker smoke profile passed
• ELF reduced Docker backfill profile passed
• cargo make checks