refactor(ui): R10 S4 — complete the selection-paint sweep (all pill idioms)

The first S4 pass migrated a subset, which left same-idiom selection pills
hand-rolled and made adjacent controls inconsistent (a /code-review finding).
This completes the sweep so every selected-among-options control shares the
recipe:

- plain pills → .pill (+ aria-pressed): Channels status filters + view tabs,
  Sidebar filter-tag chips + date presets + custom-dates, Stats tabs + ranges.
- glass-card-resting pills → .pill with the resting `glass-card glass-hover` kept
  in the non-pressed branch (solid accent when pressed): PlexSidebar library
  scope + the facet Chip (retired the round-1 "deferred" note — the recipe
  already expresses this via the resting branch, no new variant needed).
- custom-dates aria-pressed is coerced with !! so a date string can't leak into
  the attribute and miss the [aria-pressed="true"] paint.
- drop the dead `border` on ChannelTags' chip-solid (accent border on accent bg).

Out of scope (a separate concern, NOT selection-among-options): primary/action
buttons that share the accent fill — Banner action, ConfirmProvider primary,
PlexBrowse primary, PlayerModal watched-toggle — these want a future .btn-primary
recipe. Left by-design: tableHeader filter options (PopoverItem + keepSelectedPaint,
owned by the popover platform).

frontend/src/components/Channels.tsx

@@ -483,11 +483,8 @@ export default function Channels() {
         <button
           key={f.id}
           onClick={() => setStatusFilter(f.id)}
-          className={`text-xs px-2.5 py-1 rounded-full border transition ${
-            statusFilter === f.id
-              ? "bg-accent text-accent-fg border-accent"
-              : "bg-card border-border text-muted hover:border-accent"
-          }`}
+          aria-pressed={statusFilter === f.id}
+          className="pill text-xs px-2.5 py-1 rounded-full border"
         >
           {t(f.labelKey)}
         </button>
@@ -622,11 +619,8 @@ export default function Channels() {
           <button
             key={v}
             onClick={() => setView(v)}
-            className={`text-sm px-3 py-1.5 rounded-full border transition ${
-              view === v
-                ? "bg-accent text-accent-fg border-accent"
-                : "bg-card border-border text-muted hover:border-accent"
-            }`}
+            aria-pressed={view === v}
+            className="pill text-sm px-3 py-1.5 rounded-full border"
           >
             {t(`channels.tabs.${v}`)}
           </button>