WCAG AA: the hero's sign-in links read on light themes (#507)

ddiff --git a/public/index.html b/public/index.html
iindex b44117cf..12a1e680 100644
---- a/public/index.html
++++ b/public/index.html
@@@ -112,7 +112,7 @@ a{color:inherit}
  .intent.match{border-color:var(--accent);background:var(--bg-hover)}
  .intent.dim{opacity:.38}
  .hero-account{margin-top:16px;font-size:13.5px;color:var(--text-secondary)}
--.hero-account a{color:var(--accent-light);font-weight:600;text-decoration:none}.hero-account a:hover{text-decoration:underline}
++.hero-account a{color:var(--accent-light);font-weight:600;text-decoration:none}html[data-theme-mode="light"] .hero-account a{color:color-mix(in srgb,var(--accent) 62%,var(--text-primary))}.hero-account a:hover{text-decoration:underline}
  .hero-sky{position:sticky;top:72px;padding-top:24px}
  .constellation{width:100%;height:auto;display:block;overflow:visible}
  .constellation .cs-orbit{fill:none;stroke:var(--border-light);stroke-dasharray:2 6;opacity:.7}.constellation .cs-far{opacity:.4}