fix(theme): stop sun/moon overlap and restore dark float contrast

Drive toggle glyphs with html.dark/body theme classes only, drop
inline display styles that lost to !important CSS, and give the
float rail a solid surface + brighter ink in dark mode.

assets/js/core/theme.js

@@ -157,19 +157,23 @@
     syncThemeImages(isDark);
     syncCodeHighlightTheme(isDark);
     dispatchThemeChange(isDark);
+    // Icon visibility is CSS-driven via html.dark / body.theme-dark.
+    // Only sync a11y state here — do not set inline display (fights !important CSS).
     document.querySelectorAll("#theme-toggle, #theme-toggle-desktop, #theme-toggle-mobile, #dropdown-theme-toggle, #float-theme-toggle, .toggle-theme, .theme-toggle-btn, [data-action='toggle-theme']").forEach(function (btn) {
       if (!btn) return;
       btn.setAttribute("aria-pressed", isDark ? "true" : "false");
       btn.classList.toggle("is-dark", isDark);
       var moon = btn.querySelector(".theme-icon-moon, .float-btn__icon-moon");
       var sun = btn.querySelector(".theme-icon-sun, .float-btn__icon-sun");
-      if (moon && sun) {
-        // Light mode: show moon (click to go dark). Dark mode: show sun.
-        moon.style.display = isDark ? "none" : "";
-        sun.style.display = isDark ? "" : "none";
+      if (moon) {
+        moon.removeAttribute("style");
+        moon.setAttribute("aria-hidden", isDark ? "true" : "false");
+      }
+      if (sun) {
+        sun.removeAttribute("style");
+        sun.setAttribute("aria-hidden", isDark ? "false" : "true");
       }
     });
-    // Keep legacy float id path for float-btn__icon-* class names already handled above.
     var floatBtn = document.getElementById("float-theme-toggle");
     if (floatBtn) {
       floatBtn.setAttribute("aria-pressed", isDark ? "true" : "false");