fix(mobile): Ask-MSOS pill yields to cookie/language banners

In in-app browsers (Instagram/Facebook) the floating pill (z-index 9999, same
as the cookie banner) sat on top of the cookie Accept button and the language
banner, so consent could not be tapped. The pill now hides whenever the
cookie-consent (.msos-cc) or language (.lang-suggest) banner is present, via a
MutationObserver on <body>, and reappears once they are dismissed. With the
pill yielding, the language banner is dropped back to the bottom edge.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

css/components/_lang-banner.css

@@ -56,9 +56,9 @@
     .lang-suggest {
         left: 16px;
         right: 16px;
-        /* sit above the floating "Ask MSOS" pill (bottom-right, z-index above
-           this banner) so it never covers the dismiss (×) button */
-        bottom: 84px;
+        /* The Ask-MSOS pill now hides while this banner is up (see assistant.js),
+           so the banner can sit at the bottom without colliding with it. */
+        bottom: 16px;
         transform: translateY(24px);
         flex-wrap: wrap;
     }