Sharper contrast and screen-reader-friendly tables on the homepage

The marketing homepage is now easier to read and easier to navigate with assistive technology.

A couple of spots fell short of accessibility contrast guidelines: some of the small labels in the kanban preview and a few accent colors didn't stand out enough against their backgrounds, in both light and dark modes. We deepened those tones so the text passes AA contrast cleanly while keeping the same calm, muted look.

We also fixed the comparison table so screen readers can make sense of it: every column now has a proper header, and each row is labeled by its feature name. People using a screen reader hear meaningful context instead of a wall of disconnected cells.

These are the kinds of details that don't change how the page looks for most people, but make a real difference for anyone who relies on readable contrast or a screen reader.