Report benchmark task counts

[gabotechs]

Summary

• report average worker-task counts alongside each query comparison
• report the sum of per-query task averages in each dataset summary
• keep task totals visible in the benchmark bot's collapsed result view
• add a small shell utility for summing measured tasks in a stored result directory

Why

Benchmark result JSON already records the distributed worker-task count for every measured iteration, but comparisons only exposed elapsed time. Reporting both values makes parallelism changes directly visible and easier to correlate with performance.

Validation

• npm run build
• npm test (103 tests)
• bash -n benchmarks-remote/sum-tasks.sh
• ran sum-tasks.sh against an existing TPCH/SF1 result directory and recovered 920 measured tasks
• git diff --check