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>

inc/helpers/jio-float-buttons.php

@@ -168,7 +168,7 @@ if (!function_exists('jio_float_right')) :
 
 			switch ($type) {
 				case 'theme_mode':
-					$btn .= '<a' . $style . ' class="float-btn toggle-theme hover-show"' . jio_float_btn_tooltip_attr(__('切换主题', 'jio'), $is_mobile) . ' href="javascript:;"><i class="fa fas fa-toggle-theme"></i></a>';
+					$btn .= '<a' . $style . ' class="float-btn toggle-theme hover-show"' . jio_float_btn_tooltip_attr(__('切换主题', 'jio'), $is_mobile) . ' href="javascript:;"><i class="fa fa-toggle-theme"></i></a>';
 					break;
 
 				case 'back_top':