file manager: move the filter to its own row under the sort pills

Filter names (the per-service options) are long, so the label + dropdown
now live on a dedicated row below Sort.  Frontend 1152 tests green.

frontend/index.html

@@ -1117,7 +1117,8 @@
 							<span data-l10n="Sort:">Sort:</span>
 							<span class="pysim-fs-sort-pill px-2 py-0.5 rounded cursor-pointer bg-blue-600 text-white" data-fs-sort="fid" onclick="pysimFsSetSort('fid')">FID</span>
 							<span class="pysim-fs-sort-pill px-2 py-0.5 rounded cursor-pointer bg-gray-200 dark:bg-slate-700 text-gray-700 dark:text-slate-300" data-fs-sort="name" onclick="pysimFsSetSort('name')" data-l10n="Name">Name</span>
-							<span class="mx-1 text-gray-400 dark:text-slate-600">·</span>
+						</div>
+						<div class="flex items-center gap-1 mb-1 text-gray-500 dark:text-slate-400">
 							<span data-l10n="Filter:">Filter:</span>
 							<div class="relative">
 								<button type="button" id="pysim-fs-filter-btn" aria-haspopup="true" aria-expanded="false" onclick="pysimFsFilterToggle()" class="px-2 py-0.5 text-xs rounded border border-gray-300 dark:border-slate-600 hover:bg-gray-200 dark:hover:bg-slate-700 text-gray-700 dark:text-slate-300 max-w-xs truncate">All</button>