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/panelLayout.ts

@@ -16,7 +16,7 @@ export interface PanelLayout {
 // Unknown/stale ids are dropped and any missing (e.g. a group added in a later version) are
 // appended by normalizeLayout, so nothing silently disappears.
 const PANEL_ORDER: Record<PanelId, string[]> = {
-  feed: ["date", "channel", "tags", "language", "topic"],
+  feed: ["date", "year", "channel", "tags", "language", "topic"],
   plex: [
     "playlists",
     "watch",