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/index.css

@@ -474,7 +474,7 @@ body {
      .chip-solid is intentionally a PAINT-ONLY modifier (bg/text/border colour, no display or
      geometry): it sits on a site's OWN chip geometry so a truncating single-element chip
      (ChannelTags) isn't forced into inline-flex, which would break its text-overflow. Use it WITH a
-     site's `rounded-full`/`border` utilities (or on top of `.chip`), never bare. */
+     site's own geometry (`rounded-full`, optional `border`) or on top of `.chip`, never bare. */
   .chip {
     display: inline-flex;
     align-items: center;