Cross-sectional QC visualization pipeline

[nx10]

Follow-up from #301 Stage 6 scope decision.

The cross-sectional rbc qc workflow produces pass/fail metrics (motion, registration Dice, coverage) but no human-readable visual report. For release, we want a visualization layer that turns the QC TSV into something reviewable — individual-subject reports or a single-page dashboard per run.

Scope

• One HTML (or similar) report per subject-session summarizing QC outcomes.
• Registration overlay (T1w brain + template outline).
• BOLD-to-T1w coregistration overlay.
• Motion traces (FD, DVARS, RMS over time).
• Carpet plot of cleaned BOLD.
• Pass/fail summary at top with the numeric thresholds.

Exact renderer TBD (nireports, fmriplot, matplotlib-to-HTML, custom). Prefer something with minimal new deps.

Interaction with the longitudinal viz issue

Design this so longitudinal viz (tracked separately) can inherit the layout and swap in longitudinal-space overlays + inter-session reliability panels. Shared utilities should live in rbc.qc.reports or similar.

Out of scope

• Group-level reports.
• Interactive web dashboards.
• Any viz of longitudinal outputs (separate issue).

Acceptance

• rbc qc (or a new rbc qc-report subcommand — decide during implementation) produces an HTML report per subject-session alongside the existing TSV outputs.
• Covered by a smoke test asserting the HTML file exists and contains expected section headers.