fix(frontend): dashboard charts have no text alternative and layers differ only by shade #744

Summary

The dashboard chart canvases have fixed aria-labels and no text or table alternative, and the "Potential savings range" layers differ only by shade of one hue.

Where

Reviewed commit b50ca38.

• frontend/src/index.html:113, 118, 230 (<canvas role="img"> with fixed labels)
• frontend/src/dashboard.ts:909-919 ("Current", "Lowest option" and "Upside" are one hue at different alphas)

Failure scenario

A screen-reader user hears a static label and cannot read any value from the chart. A colour-blind or low-vision user cannot reliably tell the three layers apart. Verification level: subagent/source-level.

User impact

The savings charts, a headline feature of Home and Plans, are unusable without vision and hard to read with colour-vision deficiency.

Suggested fix

Add a "View as table" toggle or a visually hidden table per chart, a dynamic aria-label with key totals, and pattern or border differentiation between layers.

Related: #188 (sparse-data empty state, narrower), #189 (legend and bar-colour encoding mismatch, narrower), #700 (per-service chart colours).

Screenshots

home-full-1280.png (in the review fleet archive at /Users/cristi/.claude/agent-comms/review-fleet-20261008/screens/, NOT uploaded).

Severity

Medium: key data is inaccessible to assistive technology users.

Reviewer ID: UX-22 (usab M15)
Found by the 2026-10-08 review fleet.