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/modules/plex/PlexSidebar.tsx

@@ -21,6 +21,7 @@ import { usePlexSavedViews } from "./plexSavedViews";
 import { usePlex, usePlexActions } from "./plexContext";
 import { DismissibleChip } from "../../components/ui/Chip";
 import { Input } from "../../components/ui/Input";
+import YearPicker from "../../components/ui/YearPicker";
 import { useRail } from "../../lib/useRail";
 import { msg } from "../../lib/notifications";
 
@@ -173,18 +174,33 @@ export default function PlexSidebar() {
       id: "year",
       title: t("plex.filter.year"),
       body: (
-        <div className="flex items-center gap-2">
-          <NumberInput
-            value={filters.yearMin ?? null}
-            placeholder={facets?.year_min ?? undefined}
-            onChange={(v) => patch({ yearMin: v })}
-          />
-          <span className="text-muted text-xs">–</span>
-          <NumberInput
-            value={filters.yearMax ?? null}
-            placeholder={facets?.year_max ?? undefined}
-            onChange={(v) => patch({ yearMax: v })}
-          />
+        <div className="flex flex-col gap-2">
+          {/* One year is a range of one: picking it sets both ends, as the year on an info page does,
+              so the range fields below show it and a decade stays typeable there. */}
+          {facets && facets.years.length > 0 && (
+            <YearPicker
+              years={facets.years}
+              selected={
+                filters.yearMin != null && filters.yearMin === filters.yearMax
+                  ? filters.yearMin
+                  : undefined
+              }
+              onPick={(year) => patch({ yearMin: year ?? null, yearMax: year ?? null })}
+            />
+          )}
+          <div className="flex items-center gap-2">
+            <NumberInput
+              value={filters.yearMin ?? null}
+              placeholder={facets?.year_min ?? undefined}
+              onChange={(v) => patch({ yearMin: v })}
+            />
+            <span className="text-muted text-xs">–</span>
+            <NumberInput
+              value={filters.yearMax ?? null}
+              placeholder={facets?.year_max ?? undefined}
+              onChange={(v) => patch({ yearMax: v })}
+            />
+          </div>
         </div>
       ),
     },