homepage: capability equivalence on the AI cards

Every fleet model card (and the #models docs section) now states, in
plain family-facing terms, what the model is equivalent to:
frank-large ~ Claude Sonnet 5 / OpenAI-Luna, frank-primary ~ Claude
Opus 4.8 / OpenAI-Terra (both Summer 2026 frontier), frank-secondary ~
last year (2025) frontier. Rendered as a new details.equiv line
(desc-equiv, styled in the head color, bare-mode clean); pinned in
homepage_config.bats.

shared/homepage/style.css

@@ -81,6 +81,7 @@ body::before {
 .desc { color: var(--fg); margin: 8px 0; }
 .desc-role { color: var(--dim); font-weight: bold; }
 .desc-spec { color: var(--fg); }
+.desc-equiv { color: var(--head); font-style: italic; }
 .desc-inputs { color: var(--dim); }
 .desc-use { color: var(--fg); margin-top: 4px; }
 .links a { color: var(--link); text-decoration: underline; margin-right: 12px; }
@@ -118,6 +119,6 @@ html[data-bare="1"] body { background: #fff; color: #000; font-family: serif; te
 html[data-bare="1"] body::before { display: none; }
 html[data-bare="1"] .panel, html[data-bare="1"] .top, html[data-bare="1"] .foot { border-color: #000; background: none; }
 html[data-bare="1"] .badge, html[data-bare="1"] .name, html[data-bare="1"] .desc, html[data-bare="1"] .summary, html[data-bare="1"] .section-title { color: #000; }
-html[data-bare="1"] .desc-role, html[data-bare="1"] .desc-spec, html[data-bare="1"] .desc-inputs, html[data-bare="1"] .desc-use { color: #000; font-weight: normal; }
+html[data-bare="1"] .desc-role, html[data-bare="1"] .desc-spec, html[data-bare="1"] .desc-inputs, html[data-bare="1"] .desc-use, html[data-bare="1"] .desc-equiv { color: #000; font-weight: normal; }
 html[data-bare="1"] .section-title { border-color: #000; }
 html[data-bare="1"] .links a, html[data-bare="1"] .toggle, html[data-bare="1"] .foot a { color: #000; }