benchmark: q5 ground truth

[GnaneshGnani]

Q5 — Realized volatility σ proxy (DDSketch IQR/1.349)

Adds ground truth and 60-minute accuracy benchmark for Q5: realized volatility approximated as IQR/1.349 from DDSketch quantiles.

Benchmark results

Setup: Day 08-11-21, data_filtered, accuracy_sla=0.01, 12 × 5-min windows
Sketch: DDSketch, relative_accuracy=0.01, quantiles [0.25, 0.75]
Metric: fraction of symbols where |sketch_σ − exact_σ| / max(...) < 10%.

Windows	Pass rate	Verdict
12 (09:00–10:00 CET)	3 / 12	⚠️ Fails early market-open; passes from ~09:45

Clear warm-up pattern: at market open intraday price moves are larger and more skewed, violating the near-normal IQR/1.349 assumption. By 09:45 the distribution settles and the fraction climbs above 90%. Windows 09:45–10:00 score 0.909, 0.916, 0.910.

Cumulative: Q1: 11/12 ⚠️ | Q3: not run | Q4: 12/12 ✅ | Q5: 3/12 ⚠️

See results/benchmarking.md for per-window breakdown.

[zzylol]

Closing — this branch is conflicting with main (badly diverged, ~32k-line deletions) and predates the consolidated multi-sketch + latency eval harness merged in #494, which redid this ground-truth work. Please reopen and rebase if any ground truth here is still needed.