feat(filters): pick one year from a decade grid, in the feed and in Plex

A shared YearPicker: the recent years as chips with their counts, and a
More dialog that lays every year out by decade (sortable by count), so a
ninety-year library fits on one screen. The feed's scrolling popover gives
way to it; the Plex rail gets it above its range fields, a pick setting
both ends. The Plex facets now count titles per year, the year filter left
out.

frontend/src/lib/api/plex.ts

@@ -410,6 +410,8 @@ export interface PlexFacets {
   studios: { value: string; count: number }[]; // studio vocabulary for the sidebar picker
   // Playback-class facet (movie-only): value ∈ direct|remux|transcode_hw|transcode_sw. Empty on shows.
   playable: { value: string; count: number }[];
+  // Titles per year, newest first, the year filter itself left out (the sidebar's year picker).
+  years: { year: number; count: number }[];
   year_min: number | null;
   year_max: number | null;
   rating_max: number | null;