sandbox phase 7 (UI): pipeline rail + polish

[William-Hill]

Parent: #116 · Spec: docs/superpowers/specs/2026-05-02-sis-pdp-ar-sandbox-design.md

Scope

• Persistent horizontal rail at the top of every /sandbox/* page: SIS ── PDP ── AR ── Dashboard with state dots (filled / outlined / disabled).
• Rail is nav + breadcrumb + lineage in one component. Hover any stage shows last activity for current institution.
• One delight animation: a single gold-accent token travels left-to-right along the rail when a transformation runs.
• Final polish pass: typography, spacing, hover states, empty states, keyboard nav.

Acceptance

• Rail mounted on every /sandbox page
• Hover on each stage shows last upload metadata
• Transformation token animates exactly once per submit (no loop)
• Lighthouse a11y ≥ 95 on all sandbox routes

Estimate: 2 days. Depends on phases 4–6.