Keep the scroll fade at the screen edge on the queue's filter row

The fade that hints at more filters to the right was an element inside the
scrolling row, so it scrolled away with the chips instead of staying at the
edge; the comment on it claimed the opposite. It is now a mask on the strip
itself, applied only while there is more to scroll to (fadeOnOverflow in
ui.js sets data-more), so it stays put and disappears at the end instead of
dimming the last chip.

The Team and Admin tab strips had an always-on mask from the earlier
"Sources is cut off" fix, which dimmed their last tab even when fully
scrolled; they use the same mechanism now.

Web UI only: no endpoint or JSON shape changed, so nothing to mirror in
terdut-tui.

internal/web/static/js/admin.js

@@ -13,7 +13,7 @@
 // gate.
 
 import * as api from './api.js';
-import { h, clear, spinner, confirm, menuCard, ssoBadge, SSO_MANAGED } from './ui.js';
+import { h, clear, spinner, confirm, menuCard, ssoBadge, SSO_MANAGED, fadeOnOverflow } from './ui.js';
 import { state, myID } from './state.js';
 
 const view = () => document.getElementById('view-admin');
@@ -111,6 +111,7 @@ function subnav() {
     })));
   // On a phone the strip overflows; bring the open section into view so a
   // tab past the edge (Sources, Switches) is never the one that is hidden.
+  fadeOnOverflow(nav);
   requestAnimationFrame(() => nav.querySelector('[aria-current]')
     ?.scrollIntoView({ inline: 'center', block: 'nearest' }));
   return nav;