style(type): raise the too-small toolbar and filter text toward the view-switcher size

The view-switcher's 16px reads comfortably; the toolbar and filter controls sat at 12px. Bring
the marked controls up to match, and lift the general scale on the shared filter surfaces.

- Toolbar (feed + channel + Plex, via the shared components): FilterSelect and SortControl trigger
  pills text-xs → text-base (16px, the view-switcher size); the result count → text-sm; the
  active-filter chips → text-sm with the "FILTERED BY" label text-2xs → text-xs.
- Filterbar: the Combobox picker input → text-base (matching the toolbar pills) + its chips → text-sm;
  the panel/widget headers (SidePanel collapsed-rail + panel title, PanelGroup widget titles) up one step.

Channel info and the manager tables were already at 14–16px (readable), so they were left as-is.

frontend/src/components/PanelGroup.tsx

@@ -56,7 +56,7 @@ export default function PanelGroup({
         <button
           onClick={editing ? undefined : onToggleCollapse}
           disabled={editing}
-          className="flex-1 min-w-0 flex items-center text-left select-none text-xs uppercase tracking-wide text-muted enabled:hover:text-fg transition"
+          className="flex-1 min-w-0 flex items-center text-left select-none text-sm uppercase tracking-wide text-muted enabled:hover:text-fg transition"
         >
           <span className="truncate">{title}</span>
         </button>