A 12-week distance bar chart under the profile stats header, viewer-scoped,
built on profile-stats (#539). Design records the same no-cache rationale: one
indexed grouped aggregate over a 12-week slice (≤12 rows), gap-filled in JS.
Validates with `openspec validate --strict`. Specs only; no code.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
