[web] Use content-secondary for plan card body text (#33466)

Plan cards inherited neutral-60 (=neutral-60) for description and
include-list text, which can fail WCAG contrast on the light card
background. Switch to content-secondary (=neutral-70) per Vee's
short-term recommendation; affects the free plan description, card
include items (e.g. "Basic AI allowance") and the in-card group
picker labels.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
GitOrigin-RevId: 42aff473a779b4b4f36b6c648d86097a79f820c8

services/web/frontend/stylesheets/pages/plans-2026.scss

@@ -220,7 +220,7 @@
       background-color: var(--bg-light-primary);
       border: 1px solid var(--neutral-30);
       border-radius: var(--border-radius-medium);
-      color: var(--neutral-60);
+      color: var(--content-secondary);
       display: grid;
       grid-row: span 4;
       grid-template-rows: subgrid;
@@ -340,7 +340,7 @@
     }
 
     .card-description {
-      color: var(--neutral-60);
+      color: var(--content-secondary);
       margin-block: 0;
     }