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/feedquery.py

@@ -437,6 +437,26 @@ def feed_summary(db: Session, user: User, **params) -> dict:
     return {"count": count, "facets": facets}
 
 
+def feed_years(db: Session, user: User, **params) -> list[dict]:
+    """Per-year video counts for the current filter context (item 8 / E8·S2): powers the year control's
+    quick chips + the "more…" per-year-counts dialog. Every OTHER filter (tags, channels, content type,
+    search, watch state, scope) still applies, but the publish-date narrowing itself is DROPPED —
+    published_after/before and max_age_days — so the year list is the full set of years available and
+    switching years stays a live drill-down (the same principle as the tag facets dropping their own
+    category). One grouped query, newest year first."""
+    base, _rank = filtered_query(
+        db,
+        user,
+        **{**params, "published_after": None, "published_before": None, "max_age_days": None},
+    )
+    pub = base.with_only_columns(Video.published_at.label("pub")).subquery()
+    year = func.extract("year", pub.c.pub)
+    rows = db.execute(
+        select(year.label("y"), func.count()).group_by(year).order_by(year.desc())
+    ).all()
+    return [{"year": int(y), "count": n} for y, n in rows if y is not None]
+
+
 # --- Keyset (cursor) pagination ---------------------------------------------
 #
 # Each sort is described as an ordered list of key columns (expression + direction