feat(cwg): show round progress during task

[htsukamoto5]

Summary

• adds a compact participant-facing header to each C&WG game screen: Round N of 6`n- derives N from the schedule's zero-based round value and the total from the existing TRIALS constant, so it remains correct if the study length changes
• leaves task roles, stimuli, timing, data collection, and terminal routing unchanged

Validation

ode tests/round-progress.test.mjs`n-
ode tests/pipeline.test.mjs (39/39)

ode tests/exits.test.mjs (31/31)

ode tests/dropout.test.mjs (18/18)

• embedded C&WG script parse check

Scope

A small study-polish packet intentionally based directly on PR #18, independent of the JATOS integration work in PR #21.

[htsukamoto5]

Closing unmerged because the first paid-study target moved from C&WG to Hawkins. Hawkins already has its own fidelity/progress display work in #19, and the paid-pilot replacement path is #24.