Rename /person to /people, simplify cast to actors-only, and polish UI

Rename the person detail route from `app/(pages)/person/[id]` to
`app/(pages)/people/[id]` and update all internal links accordingly.

Strip crew members from the cast carousel so only actors are shown;
remove the `crew` prop from `CastCarousel` and `TitleCast` entirely.

Move the trailer trigger from the metadata row into a centered overlay
on the backdrop image using a new `variant="backdrop"` prop on
`TrailerDialog`, replacing the previous inline button approach.

Swap several icons for better semantic matches: `IconBooks` for the
library section, `IconCheck` for the "Mark Watched" button,
`IconSparkles` on the Recommendations heading, and `IconDeviceTvOld`
on the Seasons heading.

Replace a nested `motion.p` with a plain `<p>` using CSS
`transition-opacity` in `StatsDisplay`. Remove the `animate-gentle-float`
keyframe and the `feed-scroll` utility from `globals.css`, replacing the
latter with the existing `no-scrollbar` class.

components/command-palette.tsx

@@ -91,7 +91,7 @@ export function CommandPalette() {
     (result: SearchResult) => {
       setCommandPaletteOpen(false);
       if (result.type === "person") {
-        router.push(`/person/tmdb-${result.tmdbId}`);
+        router.push(`/people/tmdb-${result.tmdbId}`);
       } else {
         router.push(`/titles/tmdb-${result.tmdbId}-${result.type}`);
       }