fix(nav): render the theme toggle with the outline sun/moon face

The top-bar theme switch looked heavier and larger than the icons beside it.
An earlier commit dropped the `far` modifier from fa-toggle-theme, which moved
the glyphs to the Solid face. The reference's glyphs are the outline variants
(FA4's sun-o / moon-o), and in FA5 those live in the Regular face — so the
Solid replacement reads bolder and visually bigger at the same 1em size, while
the neighbouring account icons stay on the lighter Regular-style SVG set.

Restore `fa far fa-toggle-theme` on all three placements: desktop navbar,
mobile header, and the floating rail. The .fa-toggle-theme::before/::after
composite rules only handle positioning and the slide transition, so they are
unaffected by the face swap.

legacy-navigation-contract already asserts `fa far fa-toggle-theme` and passes
again; full suite 999/1000 with the pre-existing frontend-lifecycle failure.

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 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 far fa-toggle-theme"></i></a>';
 					break;
 
 				case 'back_top':