fix(frontend): core color tokens fail WCAG AA contrast #696

Summary

Core color tokens fail WCAG AA contrast. Measured ratios: savings green 3.06:1, .text-muted 2.54:1, warning badge 3.46:1, .error text 3.33:1, destructive white-on-red 3.92:1, GCP badge 3.56:1, sort icons 1.82:1 (AA needs 4.5:1 for text, 3:1 for icons/large text).

Where

Reviewed commit b50ca38.

• frontend/src/styles/base.css:27-38,107,120-121
• frontend/src/styles/components.css:149,261,603,617,1145,1316
• frontend/src/styles/tables.css:131

Failure scenario

Measured independently by the visual reviewer (computed styles) and the usability reviewer (axe, live app). Users with low vision cannot reliably read savings figures, muted help text, error messages, badges or sort indicators.

Suggested fix

Add darker -fg text tokens (for example #15803d green, #b45309 amber, #c5221f red), set muted text to #6b7280 or darker, darken the destructive and GCP badge backgrounds, and darken the sort icons.

Related: #191 (asks to verify muted/placeholder grey against WCAG AA; the measured failures here are new and broader).

Severity

High: accessibility failures in shared tokens affect every page. The usability reviewer rated it medium.

Reviewer ID: VIS-03 (vis H3 + usab M18)
Found by the 2026-10-08 review fleet.