[A11y] Audit and fix color contrast issues

[bhf]

As identified in the accessibility review (a11y.md):

Observation:

• The application uses oklch color spaces.
• Dark mode text colors (e.g., dark:text-[oklch(0.78_0.19_70)]) in DashboardContent.tsx need verification against background colors.
• Red error backgrounds (bg-red-50, dark:bg-red-900/20) need to ensure text within them maintains 4.5:1 contrast.

Action Item:

• Audit specific oklch values in DashboardContent.tsx hardcoded styles.
• Adjust colors to meet WCAG AA standards (4.5:1 contrast ratio for normal text).

Reference: Issue #6