Select on [dir='rtl'] now that no build rewrites :dir()

Plan step 39 (part 4). With Tailwind gone the Workbench's Vite build
still turns every `:dir(rtl)` into a long `:lang()` list (its own CSS
minifier, not Tailwind's doing — confirmed by rebuilding and grepping
the output). Every RTL mirror rule across the eleven stylesheets that
had one now selects `:is([dir='rtl'], [dir='rtl'] *)` instead, matching
`:dir(rtl)`'s own specificity (one pseudo-class) and its inherited
"this element or a descendant of one carrying the attribute" reach; the
built CSS now keeps the selector as written (no `:lang(` or `:dir(` left).

RTL browser tests drop the `lang="ar"` workaround the old rewrite
needed (ContainmentTest's side-sheet probe, LayoutTest's shared
layoutPage() helper) and set only dir="rtl"; CarouselTest's probe
already did. Feature tests asserting the selector's literal text
(Progress, Overlay, Menu, ListDetail, Icon, Carousel) updated to match.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

resources/css/layout/scaffold.css

@@ -234,7 +234,7 @@
         }
     }
 
-    [data-md-scaffold-fab]:dir(rtl) {
+    [data-md-scaffold-fab]:is([dir='rtl'], [dir='rtl'] *) {
         inset-inline-end: max(
             var(--md-scaffold-fab-margin),
             var(--material-safe-left, env(safe-area-inset-left))