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/tests/test_feed_views.py

@@ -201,6 +201,58 @@ def test_untagged_filter_keeps_only_channels_the_user_has_not_tagged(db, as_user
     assert _feed_ids(client, "show=all&untagged=true") == {"chSysv", "chNonev"}
 
 
+def test_feed_years_counts_ignore_the_date_narrowing_but_honour_other_filters(
+    db, as_user, make_user
+):
+    """The year facet (item 8 / E8·S2): `/api/feed/years` returns a per-year video count, newest first,
+    with the publish-date narrowing DROPPED (so switching years stays a drill-down) but every other
+    filter still applied (here: a channel pick)."""
+    user = make_user(email="years@example.com")
+    chans = {c: Channel(id=c, title=c, subscriber_count=10) for c in ("chX", "chY")}
+    db.add_all(chans.values())
+    db.flush()
+    # chX: 2 videos in 2024, 1 in 2022; chY: 1 in 2023 (should drop once we scope to chX).
+    spread = {
+        "chX": [(2024, 1), (2024, 2), (2022, 5)],
+        "chY": [(2023, 3)],
+    }
+    for cid, dates in spread.items():
+        db.add(Subscription(user_id=user.id, channel_id=cid, priority=0, hidden=False))
+        for i, (yr, day) in enumerate(dates):
+            db.add(
+                Video(
+                    id=f"{cid}v{i}",
+                    channel_id=cid,
+                    published_at=datetime(yr, 1, day, tzinfo=timezone.utc),
+                    title=f"{cid} clip {i}",
+                    is_short=False,
+                    live_status="none",
+                    via_search=False,
+                    via_explore=False,
+                )
+            )
+    db.commit()
+    client = as_user(user)
+
+    # All channels: every year present, counted, newest first.
+    resp = client.get("/api/feed/years?show=all")
+    assert resp.status_code == 200, resp.text
+    assert resp.json()["years"] == [
+        {"year": 2024, "count": 2},
+        {"year": 2023, "count": 1},
+        {"year": 2022, "count": 1},
+    ]
+
+    # A channel filter narrows the year list; a date narrowing is ignored (the point of the facet — so
+    # a selected year never zeroes out the others). Scoping to chX drops 2023, keeps 2024 (×2) + 2022.
+    resp = client.get("/api/feed/years?show=all&channel_ids=chX&published_after=2024-01-01")
+    assert resp.status_code == 200, resp.text
+    assert resp.json()["years"] == [
+        {"year": 2024, "count": 2},
+        {"year": 2022, "count": 1},
+    ]
+
+
 @pytest.mark.parametrize("case", _SUMMARY_CASES)
 def test_feed_summary_matches_count_plus_facets(db, as_user, make_user, case):
     # /feed/summary must return byte-identical numbers to the old /feed/count + /facets it replaces,