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.

assets/css/frontend/header-userbox.css

@@ -7,27 +7,22 @@
  * shell anchoring plus the account action-row geometry.
  */
 
-/* The desktop action cluster owns one horizontal alignment context. */
-.navbar-top .aksrt-navbar-actions {
-  display: flex;
-  align-items: center;
-  gap: 10px;
-  min-height: 50px;
-  margin-top: 0;
-  margin-bottom: 0;
-  padding: 0;
-}
-
-.navbar-top .aksrt-navbar-actions > *,
-.navbar-top .aksrt-navbar-account,
-.navbar-top .aksrt-navbar-account > li {
+/* The reference keeps the right cluster as three floated .navbar-form groups, so
+ * only the account row carries its own alignment context; the button groups
+ * inherit their geometry from .navbar-top .navbar-but .but and .navbar-form. */
+.navbar-top .aksrt-navbar-account {
   display: inline-flex;
   align-items: center;
-  flex: 0 0 auto;
+  gap: 4px;
+  min-height: 50px;
+  margin: 0;
 }
 
 .navbar-top .aksrt-navbar-account > li {
   position: relative;
+  display: inline-flex;
+  align-items: center;
+  flex: 0 0 auto;
   padding: 0;
   overflow: visible;
 }
@@ -40,16 +35,6 @@
   margin: 0;
 }
 
-.navbar-top .aksrt-navbar-account {
-  gap: 4px;
-  min-height: 50px;
-  margin: 0;
-}
-
-.navbar-top .aksrt-navbar-account.navbar-text {
-  float: none;
-}
-
 .navbar-top .aksrt-nav-icon,
 .navbar-top .aksrt-nav-avatar {
   display: inline-flex !important;
@@ -82,13 +67,13 @@
   object-fit: cover;
 }
 
-.navbar-top .aksrt-navbar-actions .toggle-radius {
+.navbar-top .navbar-form .toggle-radius {
   flex: 0 0 29px;
   margin: 0;
   vertical-align: middle;
 }
 
-.navbar-top .aksrt-navbar-language {
+.navbar-top .navbar-form .aksrt-navbar-language {
   margin: 0;
 }
 
@@ -96,7 +81,7 @@
  * absolutely positioned .sub-vip-card takes its normal-flow static position.
  * The shared action cluster otherwise forces inline-flex on every child, which
  * would move that static position to the flex container's cross-start. */
-.navbar-top .aksrt-navbar-actions > .hover-show {
+.navbar-top .navbar-but > .hover-show {
   display: inline-block;
 }