fix(ui): E31 S2 — the tab names the object, the channel header wraps, the player fits a short window

- The browser tab names the place and the object: PageHeading reports the
  view's own title (lib/documentTitle), so a channel, playlist or any Plex
  view reads "<object> · <module> · Siftlode" however it was opened; the
  Feed is named too; a season adds its show (tabTitle).
- The channel page's tab + action row wraps and lets the tag lane fold into
  "+N": at 1024 it ran past the edge and the page scrolled sideways.
- The YouTube player card's width is capped from the window height less the
  chrome measured under the video: at 133% zoom (685px) it cut its channel row.
- Plex certificate words (Not Rated, Approved, Passed) are named through the
  vocabulary on the info badge, show page, collection, filter and chips.
- DESIGN.md: the zoom target is 125% and 133%, not 200% (decision log).

frontend/src/components/PlexInfo.tsx

@@ -187,7 +187,7 @@ function FactsPanel({
       label: t("plex.info.facts.cert"),
       node: (
         <Filterable tag onClick={onFilter ? () => onFilter({ contentRatings: [cert] }) : undefined}>
-          {cert}
+          {vocab(t, "certificate", cert)}
         </Filterable>
       ),
     });
@@ -589,7 +589,7 @@ export default function PlexInfo({
                         : undefined
                     }
                   >
-                    {detail.content_rating}
+                    {vocab(t, "certificate", detail.content_rating)}
                   </Filterable>
                 )}
                 {detail.duration_seconds ? (