Hide the scrollbar on the person-switcher chip row

Still scrolls the same way, just without the visible scrollbar chrome --
a new .scrollbar-hide utility (scrollbar-width/-ms-overflow-style plus
the WebKit pseudo-element) rather than anything scroll-behaviour-affecting.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ECGMEwrc2k4D8VQuwjstj9

mobile/templates/mobile/base.html

@@ -72,7 +72,7 @@
             </div>
 
             {% if managed_people|length > 1 %}
-                <div class="mt-3 flex gap-2 overflow-x-auto pb-0.5">
+                <div class="scrollbar-hide mt-3 flex gap-2 overflow-x-auto pb-0.5">
                     <a class="person-chip {% if scope_everyone %}person-chip-active{% endif %}" href="?as=all">
                         <span class="person-chip-avatar">
                             <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.2" stroke-linecap="round" stroke-linejoin="round"><circle cx="8" cy="8" r="3"/><circle cx="17" cy="9" r="2.6"/><path d="M2.5 20c0-3.3 2.5-5.6 5.5-5.6s5.5 2.3 5.5 5.6"/><path d="M14 15c2.6.3 4.5 2.3 4.5 5"/></svg>