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.

tests/navigation/legacy-navigation-contract.test.cjs

@@ -225,8 +225,11 @@ test('the account popover rows match the reference user box structure', () => {
   assert.match(header, /but block c-yellow is-done/);
   assert.match(buttonsCss, /\.but\.block\s*\{\s*display:\s*block;\s*\}/);
   assert.match(buttonsCss, /\.btn-block\s*\{\s*display:\s*block;\s*width:\s*100%;\s*\}/);
-  assert.match(legacyMainCss, /\.navbar-top \.navbar-but > \.but\s*\{[^}]*font-size:\s*0\.8em;[^}]*padding:\s*0\.3em 1em !important;[^}]*margin:\s*0\.4em;/s);
-  assert.doesNotMatch(legacyMainCss, /\.navbar-top \.navbar-but \.but\s*\{/);
+  // The reference selector is a descendant, so the VIP chip inside its hover-show
+  // wrapper receives the same .but geometry (font-size, padding, margin) as the
+  // publish chip instead of falling back to the bare .but defaults.
+  assert.match(legacyMainCss, /\.navbar-top \.navbar-but \.but\s*\{[^}]*font-size:\s*0\.8em;[^}]*padding:\s*0\.3em 1em !important;[^}]*margin:\s*0\.4em;/s);
+  assert.doesNotMatch(legacyMainCss, /\.navbar-top \.navbar-but > \.but\s*\{/);
   assert.doesNotMatch(header, /but block c-yellow[^"']*btn-block/);
   assert.match(header, /<div class="mt6 em09" style="padding:2px;">' \. \$checkin \. '<\/div>/);
   assert.match(header, /data-signin-done-label[\s\S]{0,120}?今日已签到/);