design(board): dim completed rows in the list so they recede

[johnpc]

Design-polish pass — continuing on the List view (per owner direction). With "Show completed" on, a done row only struck through and dimmed its title — the rest of the row (assignee, due date, colored priority pill) stayed at full active strength. So completed tasks still competed visually with open ones, and the eye couldn't quickly separate done from not-done.

Fix (CSS-only, tokens only)

Dim the entire completed row (opacity: 0.6) so it recedes as a whole — title, meta columns, and priority pill fade together. The green complete-ring stays clearly legible even dimmed, and the row returns to full opacity on hover so it's easy to edit or un-complete. Now open tasks stand out crisply while done tasks sit quietly (the Asana pattern).

Before → after

Before: only the done row's title was struck; its "Medium" pill / dates still popped like an active task.
After (whole done row recedes, open tasks lead):

• Desktop: https://files.jpc.io/d/LkwkA-list-done-dim-desktop.png
• Mobile: https://files.jpc.io/d/GjYHa-list-done-dim-mobile.png

(Done rows are hidden by default; this affects the "Show completed" view.)

Full quality gate green; presentational-only. Verified against the sandbox (AWS_PROFILE=personal).