Longitudinal QC visualization pipeline

[nx10]

Follow-up from #301 Stage 6 scope decision.

The longitudinal pipeline's minimal QC (Dice + pass/fail on session-to-template registration) covers the numerical side. For release-grade output we also want a visual report, paired with the cross-sectional viz work.

Scope

Build on top of the cross-sectional viz infrastructure (see related issue, filed alongside). Longitudinal-specific additions:

• Session-to-longitudinal-template registration overlays (one panel per session).
• Longitudinal-space BOLD coverage across sessions (mask overlap map).
• Inter-session reliability panel: within-subject ALFF / ReHo consistency across sessions (e.g. voxel-wise Spearman, or per-ROI test-retest ICC).
• Per-session motion summary side-by-side so reviewers can spot sessions that should be excluded.

Dependencies

• Cross-sectional viz pipeline landing first (shared report infra, layout, renderer choice).
• Longitudinal pipeline: refactor and release readiness (tracker) #301 Stage 6 landing (the numerical QC that feeds the plots).

Out of scope

• Group-level longitudinal analysis reports.
• Anything that requires more than 2 sessions in the fixture.

Acceptance

• rbc longitudinal qc produces an HTML report per subject summarizing all sessions' alignment.
• Smoke test on the ds000114 fixture.