Deepen DESIGN.md gallery treatment

[peterabcd]

Summary

• HeroBand: centered/compact variants, larger display scale (up to 76px), accent eyebrows (Action Blue / Sky Link Blue per DESIGN.md dark-surface rule)
• New SiteFooter (parchment, dense-link columns, fine print) wired into the root layout
• New StatStrip in the home hero showing real archive numbers (sessions, total km, runners) instead of placeholder cells
• Archive: compact hero with real session count; removed mock summary cells
• SessionCard: full-bleed photo, frosted participant chip overlay, gallery typography
• Login/pending centered heroes; session detail and runner pages use compact heroes

Verification

• pnpm run test (20 passed)
• pnpm run typecheck
• pnpm run lint
• pnpm run build
• pnpm run test:e2e (3 passed)