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.

backend/app/routes/feed.py

@@ -14,6 +14,7 @@ from app.feedquery import (
     decode_cursor,
     encode_cursor,
     feed_summary,
+    feed_years,
     filtered_query,
     keyset_predicate,
     order_by,
@@ -206,6 +207,19 @@ def get_feed_summary(
     return feed_summary(db, user, **params)
 
 
+@router.get("/feed/years")
+def get_feed_years(
+    params: dict = Depends(_feed_params),
+    user: User = Depends(current_user),
+    db: Session = Depends(get_db),
+) -> dict:
+    """Per-year video counts for the year control (item 8 / E8·S2): the quick recent-year chips and the
+    "more…" per-year-counts dialog. Every filter EXCEPT the publish-date narrowing applies, so picking a
+    year re-queries the feed but not this list. Response: {"years": [{"year": <int>, "count": <int>}]},
+    newest year first."""
+    return {"years": feed_years(db, user, **params)}
+
+
 class VideoStateIn(BaseModel):
     status: str