fix(header): restore reference VIP chip geometry and cluster split

The VIP chip never received the reference .but geometry. Commit f03d72c8
narrowed the legacy selector from a descendant to a child combinator as a
side effect of an unrelated user-popover fix, and the contract test then
pinned the narrowed form. Because the VIP anchor lives inside the
hover-show wrapper rather than being a direct child of .navbar-but, it
fell back to the bare .but defaults: 15px type instead of 0.8em, no
0.4em margin, and no padding override.

Restore the descendant selector so both chips share one geometry:

- .navbar-top .navbar-but .but is byte-identical to the reference again,
  giving the VIP chip font-size 0.8em, padding 0.3em 1em !important and
  margin 0.4em
- the publish and VIP anchors are plain inline-block .but elements again
  (the merged flex container no longer blockifies them)
- ml10 is back on the VIP anchor; .navbar-top .navbar-but .but overrides
  it exactly as it does in the reference, so it stays markup parity
  without changing the computed margin

The right cluster was also merged into one .aksrt-navbar-actions flex
container with a 10px gap and zero padding, while the reference emits
three floated .navbar-form.navbar-right groups whose 15px padding is what
produces the inter-cluster spacing. Split them again: publish/VIP in
.navbar-but, theme toggle plus language switcher in a flex ac group, and
the account row in its own group. Measured against the reference, the
publish-to-VIP gap was 19.6px instead of 9.6px, and VIP-to-theme-toggle
was 14.8px instead of 34.8px.

The container rules in header-userbox.css are re-anchored onto the
reference structure: .aksrt-navbar-account owns the only remaining flex
context, .toggle-radius and .aksrt-navbar-language are scoped through
.navbar-form, and the hover-show rule targets .navbar-but. Coverage of
those selectors is unchanged, so the theme toggle, language switcher and
message icon keep their current geometry.

The .aksrt-navbar-actions wrapper and its gap are gone; a negative
assertion now guards against reintroducing them.

Verified: node --test across tests/ (603 passing), php -l on the changed
PHP files, and a stubbed render of aksrt_menu_button() for guest,
logged-in and layout 2.

inc/helpers/aksrt-header-menu-buttons.php

@@ -119,7 +119,7 @@ if (!function_exists('aksrt_render_header_menu_buttons')) :
 				}
 				// legacy: span.hover-show wraps button + .sub-menu.sub-vip-card
 				$html .= '<span class="hover-show inline-block">';
-				$html .= '<a class="' . esc_attr($cls) . ' but jb-red radius payvip-icon" href="javascript:;">'
+				$html .= '<a class="' . esc_attr($cls) . ' but jb-red radius payvip-icon ml10" href="javascript:;">'
 					. '<svg class="em12 mr3" aria-hidden="true"><use xlink:href="#icon-vip_1"></use></svg>'
 					. esc_html__('开通会员', 'aksrt') . '</a>' . $hover . '</span>';
 			}

inc/helpers/header/aksrt-header-navbar.php

@@ -303,6 +303,12 @@ if (!function_exists('aksrt_menu_button')) :
 	/**
 	 * Right cluster: fold, publish/VIP, theme, user, search (legacy).
 	 *
+	 * The reference splits the cluster into three floated .navbar-form
+	 * groups (publish/VIP, theme + language, account row). Each group
+	 * keeps its own .navbar-form padding, which is what produces the
+	 * reference inter-cluster spacing, so the groups are emitted
+	 * separately instead of being merged into one flex container.
+	 *
 	 * @param array<string,mixed> $ctx
 	 */
 	function aksrt_menu_button(array $ctx): void {
@@ -371,14 +377,24 @@ if (!function_exists('aksrt_menu_button')) :
 		$account = '<ul class="list-inline splitters relative aksrt-navbar-account'
 			. ($user_id <= 0 && '2' === $layout ? ' navbar-text' : '') . '">'
 			. $notification_but . $sign_but . $search_but . '</ul>';
-		$button = '<div class="aksrt-navbar-actions navbar-form navbar-right navbar-but">'
-			. $actions . $utility_buttons . $account . '</div>';
+
+		// Reference cluster split: publish/VIP, theme + language, account row.
+		$button = '';
+		if ($actions !== '') {
+			$button = '<div class="navbar-form navbar-right navbar-but">' . $actions . '</div>';
+		}
+		if ($utility_buttons !== '') {
+			$button .= '<div class="navbar-form navbar-right flex ac">' . $utility_buttons . '</div>';
+		}
+		$right_but = '<div class="navbar-form navbar-right'
+			. ($user_id <= 0 && '2' === $layout ? ' navbar-text' : '') . '">'
+			. $account . '</div>';
 
 		$fold = '<div class="navbar-form navbar-right hide show-nav-but" style="margin-right:-10px;">'
 			. '<a data-toggle-class data-target=".nav.navbar-nav" href="javascript:;" class="aksrt-nav-icon" aria-label="'
 			. esc_attr__('展开菜单', 'aksrt') . '"><svg class="icon" viewBox="0 0 1024 1024" aria-hidden="true"><use xlink:href="#icon-menu_2"></use></svg></a></div>';
 
-		$html = $fold . $button;
+		$html = $fold . $button . $right_but;
 
 		echo $html; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped
 	}