fix(nav): restore reference theme toggle geometry and single binding

The top-bar theme switch was bound twice — core/theme.js attached a click
handler to #theme-toggle-desktop while runtime/main.js delegated click on
.toggle-theme, and both ship in main.min.js, so one press toggled twice and
the button looked dead.

Also realign the control with the reference:

- Drop the far modifier from fa-toggle-theme so the sun/moon glyphs resolve
  against the Solid face at the reference weight instead of Regular.
- Restore .toggle-radius .fa/.icon to the reference form (left/right 0 +
  auto margin only). The extra position/top/transform/size/flex block and
  the > i selector were overriding the shared abs-* centering rule.
- Replace the per-ID bindings with one delegated listener so the floating
  rail, which carries no id, keeps working.
- Remove dead theme.js queries for selectors no markup or stylesheet ships
  (#theme-toggle, #dropdown-theme-toggle, .theme-icon-moon/.theme-icon-sun,
  [data-action='toggle-theme'], .is-dark).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

assets/js/core/theme.js

@@ -157,25 +157,11 @@
     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, .toggle-theme, [data-action='toggle-theme']").forEach(function (btn) {
-      if (!btn) return;
+    // Glyph visibility (sun / moon slide) is CSS-driven off .toggle-theme's
+    // ::before / ::after and the .dark-theme body class — no JS here.
+    document.querySelectorAll(".toggle-theme").forEach(function (btn) {
       btn.setAttribute("aria-pressed", isDark ? "true" : "false");
-      btn.classList.toggle("is-dark", isDark);
-      var moon = btn.querySelector(".theme-icon-moon");
-      var sun = btn.querySelector(".theme-icon-sun");
-      if (moon) {
-        moon.removeAttribute("style");
-        moon.setAttribute("aria-hidden", isDark ? "true" : "false");
-      }
-      if (sun) {
-        sun.removeAttribute("style");
-        sun.setAttribute("aria-hidden", isDark ? "false" : "true");
-      }
     });
-    var ddBtn = document.getElementById("dropdown-theme-toggle");
-    if (ddBtn) ddBtn.setAttribute("aria-pressed", isDark ? "true" : "false");
   }
 
   var themeInitialized = false;
@@ -243,20 +229,15 @@
       }
     }
 
-    function bindToggle(id) {
-      var el = document.getElementById(id);
-      if (!el) return;
-      el.addEventListener("click", function (event) {
-        var next = document.body.classList.contains("theme-dark") ? "light" : "dark";
-        setStoredTheme(next);
-        runThemeTransition(next, event);
-      });
-    }
-
-    bindToggle("theme-toggle");
-    bindToggle("theme-toggle-desktop");
-    bindToggle("dropdown-theme-toggle");
-    bindToggle("theme-toggle-mobile");
+    // Delegated so every current and future .toggle-theme anchor works — the
+    // header, the mobile drawer and the floating rail all share one binding.
+    document.addEventListener("click", function (event) {
+      var btn = event.target && event.target.closest ? event.target.closest(".toggle-theme") : null;
+      if (!btn) return;
+      var next = document.body.classList.contains("theme-dark") ? "light" : "dark";
+      setStoredTheme(next);
+      runThemeTransition(next, event);
+    });
   }
 
   if (document.readyState === "loading") {