feat(feed): filter by year — per-year count facet + year control (E8·S2)

Add a Year filter to the feed rail: quick chips for recent years plus a
'More…' popover listing all years with per-year video counts, sortable by
year or count. Selecting a year narrows the feed to that whole calendar
year (a published_after/before range applied in the api layer) and is
mutually exclusive with the Upload-date control.

Backend: new /api/feed/years endpoint + feed_years() — one grouped query
that honours every filter EXCEPT the publish-date narrowing (dropped), so
the year list stays a live drill-down and switching years never zeroes the
others. FE keys the list on the date-stripped filters, so picking a year
re-queries the feed but not the list.

Wires year through FeedFilters, the filterParams/URL (?year) round-trip,
the active-filter chip row, and the panel layout. i18n HU+EN.

Tests: feed_years count query (date narrowing ignored, other filters
honoured); dateFilter year-clearing; urlState year round-trip.

frontend/src/lib/urlState.ts

@@ -25,6 +25,7 @@ const KEYS = [
   "maxage",
   "from",
   "to",
+  "year",
   "mindur",
   "maxdur",
 ] as const;
@@ -50,6 +51,7 @@ export function filtersToParams(f: FeedFilters): URLSearchParams {
   if (f.maxAgeDays) p.set("maxage", String(f.maxAgeDays));
   if (f.dateFrom) p.set("from", f.dateFrom);
   if (f.dateTo) p.set("to", f.dateTo);
+  if (f.year) p.set("year", String(f.year));
   if (f.minDuration != null) p.set("mindur", String(f.minDuration));
   if (f.maxDuration != null) p.set("maxdur", String(f.maxDuration));
   return p;
@@ -102,6 +104,7 @@ export function paramsToFilters(params: URLSearchParams, base: FeedFilters): Fee
   f.maxAgeDays = num(params.get("maxage"));
   f.dateFrom = params.get("from") || undefined;
   f.dateTo = params.get("to") || undefined;
+  f.year = num(params.get("year"));
   f.minDuration = num(params.get("mindur"));
   f.maxDuration = num(params.get("maxdur"));
   return f;