Dark mode polish pass

A full audit of the dashboard in dark mode. Contrast ratios on secondary text, card borders, and status badges have all been improved. The kanban board in particular looked rough, muted backgrounds were too similar to card backgrounds, making columns hard to distinguish at a glance.

• Secondary text, contrast ratio raised from 3.1:1 to 4.7:1 across all muted text
• Card borders, increased opacity on dark backgrounds for better separation
• Status badges, New, Fix, and Improvement badges now legible on dark card backgrounds
• Kanban columns, column headers and separators now clearly distinct in dark mode

Dark mode is now part of our standard QA checklist, every new feature is reviewed in both light and dark before shipping. If you spot something that looks off, send a screenshot to hello@rolvelio.app.