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.

app/(pages)/dashboard/_components/library-section.tsx

@@ -1,4 +1,4 @@
-import { IconSparkles } from "@tabler/icons-react";
+import { IconBooks } from "@tabler/icons-react";
 import { getNewAvailableFeed } from "@/lib/services/discovery";
 import { tmdbImageUrl } from "@/lib/tmdb/image";
 import { FeedSection } from "./feed-section";
@@ -21,7 +21,7 @@ export async function LibrarySection({ userId }: { userId: string }) {
   return (
     <FeedSection
       title="In Your Library"
-      icon={<IconSparkles className="size-5 text-primary" />}
+      icon={<IconBooks className="size-5 text-primary" />}
     >
       <TitleGrid items={items} />
     </FeedSection>